Chapter 3: Prokaryotic Cells

so in this video we're gonna cover chapter three looking at functional anatomy of prokaryotic cells and in the next unit we'll move on to chapter four which is looking at eukaryotic cells but for the purpose of this one we're gonna look at prokaryotic cells [Music] first no so what you saw in the video was this big giant blob here this was a white blood cell and it was chasing a bacterium and so what we're going to learn throughout this unit is how were these cells able to do all of these different things for example how

was the white blood cell able to move how did it know where the bacteria was why did it engulf the bacteria meaning doing a process called phagocytosis to take in that foreign invader why was it able to recognize that the bacteria was foreign and the red blood cells which are these circular cells here that those cells were self how did it recognize the difference between them and so as we kind of move throughout this unit looking at prokaryotic cells and eukaryotic cells you'll really start to gain an understanding of how did these cells do these

different things what was it that allowed them to do these different things so what we're going to do to start off is we are going to talk about what are structures that are found in all cells because then we will start to break down how prokaryotic and eukaryotic cells are different but first we're going to start with what do all cells have in common and the first thing is that all cells have a plasma or cell membrane and this is a phospholipid bilayer and it separates the living cell from the non-living environment now sometimes students

want to say that all cells have a cell wall that is not true not all cells have a cell wall animal cells for example do not have a cell wall protozoan cells do not have a cell wall so we can't say cell walls but we can say all cells have a cell or plasma membrane all cells have chromosomes and chromosomes are the dna molecules that carry the genes the genes are going to be the hereditary information meaning those are the sequences of dna that code for some functional product typically that product is going to be

that it's coding for a protein in other cases it's coding for a type of rna but it codes for some sort of functional product and so all cells have chromosomes they all have to have some form of genetic material all cells have ribosomes and the ribosome is an organelle that's used to synthesize which is another word for make proteins all cells have to be able to synthesize proteins because proteins do a variety of different things within the cell they act as enzymes to speed up chemical reactions they allow cells to communicate they allow cells to

get molecules into the cell because those proteins can act as channels in the membrane etc proteins are absolutely essential therefore all cells have to be able to make proteins and therefore they all have ribosomes so whether it's bacterial cells or plant cells or animal cells they all are going to have ribosomes and then lastly all cells have cytosol and cytosol is the semi-fluid substance inside the cell membrane and this cytosol this fluid is primarily water about 70 to 95 of the cytosol is water and the rest is going to be macromolecules etc ions etc that

are dissolved in the cytosol so all cells have a cell membrane chromosomes ribosomes and cytosol so those are things that are found in all cells now we're going to break down and talk about how our cells different what do different cells have that make them different from one another so when we refer to a prokaryotic cell prokaryotic cell comes from the greek word for pre-nucleus meaning prokaryotic cells do not have a membrane-bound nucleus their dna is not contained within a separate membrane inside the cell in a prokaryotic cell the cell membrane is their membrane they

don't have a separate membrane that surrounds their genetic information eukaryotic cell comes from the greek word for true nucleus a eukaryotic cell is one that has a membrane-bound nucleus it has a membrane that surrounds the genetic information so if we compare and contrast prokaryotic and eukaryotic cells prokaryotic cells contain one or few not many though one or a few circular chromosomes so it's a circle this chromosome is not in a membrane again it's not separated by a membrane like we see for eukaryotic cells eukaryotic cells have chromosomes that are paired so like if you think

about us for example humans we have 46 chromosomes those 46 chromosomes are arranged into 23 pairs meaning 23 of your chromosomes came from mom 23 chromosomes came from dad we reproduce using sexual reproduction prokaryotic cells do not prokaryotic cells simply do asexual reproduction so their chromosomes are not paired but eukaryotic cells have paired chromosomes those paired chromosomes are linear meaning they're long strands they don't connect in a circle so they're linear chromosomes and they are contained within a nuclear membrane meaning there's a separate membrane that surrounds the genetic information so prokaryotic cells one or a

few circular chromosomes not in a membrane eukaryotic cells paired chromosomes that are linear and they are separated by a nuclear membrane prokaryotic cells do not have histones histones are a type of protein that dna wraps around and when the dna wraps around it it allows the dna to pack in very tightly prokaryotic cells their dna is not especially large and therefore they don't necessarily need histone proteins whereas eukaryotic cells have extremely long dna sequences if you were to take the dna of one of your single cells out of the cell so let's say we looked

at our cheek cell that cell is microscopic you have to use a microscope to see it however if you took the dna out of one single cheek cell and lined up your 46 chromosomes end to end meaning single file that dna would stretch over six feet long so taller than me would be how long that dna would be and that dna is able to pack in that teeny tiny cell that's microscopic and so histones help facilitate that they help the dna to pack in very tightly prokaryotic cells do not have membrane-bound organelles eukaryotic cells do

they have membrane-bound organelles so they have structures like mitochondria chloroplasts endoplasmic reticulum golgi apparatus lysosomes etc other organelles these little tiny organs within the cell that serve a specific function eukaryotic cells have them prokaryotic cells do not in terms of cell wall again not all cells have a cell wall however in prokaryotic cells the cell wall is made of peptidoglycan peptido refers to protein glycan refers to sugar so in the case of bacteria their cell wall is made of this peptidoglycan it's this protein sugar mix most bacteria have peptidoglycan in their cell walls there are

some exceptions but again we're going to go with general rules in archaea if you recall back to chapter one when we talked about archaea archaea are prokaryotic cells they are typically they're more likely to be what we call extremophiles meaning they live in extreme environments and in the case of archaea their cell walls are made of something called pseudomurin it's actually very similar to peptidoglycan it is still protein sugar mix but it is in fact distinct from peptidoglycan and so that's something that's different between bacteria and archaea in terms of eukaryotic cell walls eukaryotic cell

walls if they have them again not all do they would be made of typically polysaccharides polysaccharides means many sugars linked together for fungi this would be chitin and for plants and algae this would be cellulose these are both polysaccharides and they're both found in cell walls in eukaryotic cells now again in eukaryotic cells not all categories of eukaryotic cells have a cell wall animal cells don't protozoans don't right but if they do have it typically it's going to be made of polysaccharide it's many sugars linked together in terms of the way that cells replicate in

prokaryotic cells cells divide by a process referred to as binary fission it's an asexual type of reproduction where the dna is going to duplicate and then it's going to divide into two cells in eukaryotic cells when cells go to replicate they will still replicate however the process through which they replicate is different eukaryotic cells will move chromosomes using something called the mitotic spindle this does not happen in prokaryotic cells but it does happen in eukaryotic cells and so there are some differences in the way that cells divide so what we have here is we have

a table comparing and contrasting eukaryotic and prokaryotic cells and so what i'm going to have you do and then we're going to discuss this in zoom is i'm going to have you fill this in and i want you to record so for example for nucleus you want to record for eukaryotic cells either yes or no in terms of the nucleus so eukaryotic cells do they have a nucleus yes or no prokaryotic cells do they have a nucleus yes or no same thing with membrane-bound organelles yes or no ribosomes yes or no cell membranes yes or

no cell wall yes or no and also you should be specific and say if they do have a cell wall what would it be made of for eukaryotic cells versus prokaryotic cells and then lastly we have cell size so basically what this is asking is which one is typically larger and which one is typically smaller so think about when we did our cheek cell smears for example right were our cheek cell size bigger larger or smaller than the bacteria that was on that slide so one of them you're going to write larger and the other

you're going to write smaller and so you want to fill this in and then we will have a discussion on zoom to go over this answer together so we are going to look at a functional anatomy of prokaryotes look at structures within a prokaryotic cell and talk about what these different structures do so in terms of prokaryotic cells most bacteria have an average size of about one micrometer or one micron in terms of size if we're talking about a cocci which is a sphere they have a circumference going around of approximately one micron in size

if we're talking about rods like e coli the rods typically will have a length of about 2 micrometers in size and a width of about one micrometer but on average right they're about one micrometer in size if we were to talk about a red blood cell just to give you an idea of scale a red blood cell would have a size of approximately 7.5 micrometers in size now most bacteria are what we call monomorphic mono refers to 1 morph reverse shape these are bacteria that have one shape meaning if they're rod they are always rod

shaped bacteria however there are a few bacteria that are pleomorphic meaning they have many shapes so their shape can change for example cranny bacteria they have a type of structure a shape that can change and this this is a variation in the size and the shape of the cell of a single species due to nutritional and genetic differences so depending on the resources that are available that can influence the shape of that bacteria and so that would be a type of bacteria that would be pleomorphic it has many shapes again pleomorphic would be much more

rare there aren't as many bacteria that do that most bacteria are monomorphic they have one shape so if we talk about basic shapes of prokaryotic cells we can have a rod shaped bacteria which we refer to as bacillus so singular we say bacillus if we are talking about a group of rod shaped bacteria the plural would be bacilli instead of the us it's an eye so bacilli would be plural for rod shaped bacteria if we refer to bacteria as being caucus shaped coccus shaped is going to be spherical they're spheres or round caucus is going

to be singular plural is going to be cocci so cocci would be the plural now notice when we're talking about shapes here when we talk about shapes we're talking about bacteria's morphology morphology is their shape so they could be bacillus shaped they could be caucus-shaped or they could be a spiral and so if we look at different types of spirals we can have what's called a vibrio and a vibrio is a curved rod it kind of reminds me of a comma so that would be a vibrio a spherium is a type of spiral but it's

a rigid helical shape think of it like if you've seen old telephone cords right that have that rigid um spiral that would be like spirulum it has this rigid helical shape that's in contrast to spirochete which is going to be a flexible helical shape notice it's not a perfect corkscrew it's not a perfect spiral and in fact that helix is very flexible so these are different types of morphology that bacteria can have and so typically most commonly they're going to be one of these types now when you see bacillus you need to be careful because

there is a genus so a group of organisms that are bacillus so for example if we talk about bacillus anthracis or bacillus serious bacillus is the genus that's the group of bacteria there is also bacillus the shape right and bacillus shape is going to be the rod shaped bacteria now within genus bacillus so within this genus bacteria are also bacillus shaped so those go hand in hand but not all bacteria that are bacillus shaped meaning not all raw bacteria is in the genus bacillus the genus bacillus is gram-positive and if we think about bacteria in

the gut for example like aceresia coli those are rod-shaped bacteria but estericia is the genus the genus is not bacillus so you have to be really careful when you're looking at bacillus to figure out is somebody talking about the shape bacillus or are they talking about the scientific name the genus bacillus if you see it italicized you're referring to the genus if it is not italicized it's referring to the shape and so that's typically a good way to distinguish between them or remember that for scientific names if they're hand written meaning they're not typed bacillus

would be underlined and that's how you would know it's the scientific name again that would not be the case for the shape so all bacteria in the genus bacillus are bacillus shaped but not all bacillus shaped bacteria are in the genus bacillus so you have to be really careful with when you're talking about bacillus are you talking about the shape or are you talking about the genus there are some unusually shaped bacteria that don't fall into one of those main categories that we're talking about an example of this is this star-shaped bacteria that was discovered

that is part of this genus stella and this was a type of bacteria that was discovered in the tundra in the ice in russia and so they discovered this unique bacteria that has this kind of star shape this is different right than many of the other shapes that we've seen some bacteria are rectangular they almost look like little boxes and they might appear more like a plant cell plant cells often look more boxy there are some bacteria that are also rectangular these would be part of the genus halo arcula now in addition to shape or

morphology we can also talk about bacteria bacterial arrangements meaning how do they grow in terms of groups so if they are paired pair is going to be diplo di means two so we could have diplococci or we could have diplo bacilli so they're paired up we could have clusters clusters the arrangement is referred to as staphylo so staphylo are grape-like clusters caucus is referring to spheres so we have these grape-like clusters of spherical-shaped bacteria now you're not going to see staphylobacilli you're not going to see clusters of bacillus shaped bacteria and that's because simply when

these rod shaped bacteria go to reproduce they only divide along their horizontal axis meaning they only divide out they don't divide any other direction so you're not going to see staphylobacilli but you will see staphylococci if the bacteria is in chains chains would be strepto so we could have streptococci so these are chains of spheres or we could have streptobacilli which are chains of bacillus shaped and so this is the arrangement so the cocci or the bacilli those are the morphologies the prefix the part that comes before that is the bacteria's arrangement meaning how are

multiple bacteria grouped together so what we're going to look at is we're going to start to kind of take a tour of a prokaryotic cell and talk about the different structures that are found in a prokaryotic cell so what you're looking at in this diagram and i know this is super small but these are the types of images that are in your textbook but what you're looking at here on the left these are structures that are found in all bacteria so again you'll notice that the structures that you see there are going to be the

cell membrane the bacterial chromosome ribosomes cytoplasm or cytosol those again are structures found in all cells so they're not just found in all prokaryotic cells they're actually found in all cells but in fact they're found in all prokaryotic cells as well notice that these structures on the right are only found in some bacteria meaning they're found in certain types of bacteria but they're not found in all bacteria so we will talk about an s layer we'll talk about fembrier the outer membrane cell wall cytoskeleton pili glycocalyx inclusions etc we are going to go through and

talk about a lot of these other structures that are found in only certain bacteria and we'll talk about what do each of these structures do for a prokaryotic cell so i like this diagram because it really starts to break down kind of where are these structures located so the first set of structures would be external structures things that are on the outside of the bacterial cell so we have what are called appendages so things that are coming out from the bacterial cell wall this would be things like flagella which is used for motility we have

pili which are used for something called conjugation for motility etc we have fimbriae fimbriae are used for attachment we have nanowires and nanotubes we're not going to get into those as much in this lecture we will talk about surface layers so structures on the outside of the cell wall this would include what we call an s layer and we will also talk about glycocalyx then we will talk about the boundary meaning kind of the transition between the inside of the cell and the outside being the external structures so this is right along that boundary so

this would include an outer membrane if you're talking about gram-negative bacteria this would include a cell wall this would include the cytoplasmic membrane and then we will also talk about internal structures so cytoplasm ribosomes inclusions nucleoid or chromosomes cytoskeleton endospores plasmids microcompartments etc and so we will walk through and talk about what do these different structures do what is their purpose in a bacterial cell so we are going to start with our external structures first so we're gonna go from the outside in and in fact we will actually do the cell membrane and cell wall

at the end so we're gonna do external structures first then go inside and then go to the boundary so starting with external structures we have our glycocalyx glycocalyx is a gelatinous external layer that is made of polysaccharide or polypeptide polysaccharide again is going to be sugar based polypeptide is going to be protein-based polypeptide is much less common however it is found in bacillus anthracis which is the bacteria that causes anthrax and bacillus anthracis has a glycocalyx that is made of d glutamic acid now the reason that that's important is that because it's made of this

amino acid and the amino acid is in its d isoform the l isoform of glutamic acid is the one that's more prevalent in nature meaning that's the one you see more commonly because bacillus anthraces has a glycocalyx made of d-glutamic acid which is not the typical amino acid it's a variation it's an isoform because it's glycocalyx is made of this unique d-glutamic acid the immune system can't digest it it doesn't recognize that and it's not able to digest it and as a result that gives bacillus anthracis an advantage being in the body because its outer

layer can't be digested by our immune cells and it's because it has this unique glycocalyx that is made of d-glutamic acid now when we talk about types of glycocalyx we can break it down into two categories the first type of glycocalyx would be referred to as a slime and in a slime it's loosely organized and attached to the cell so you'll notice that it's not highly organized it's not tightly adhered to the cell it's just kind of loosely attached that's in contrast to a capsule in lab we talked about a capsule stain and a capsule

is a highly organized type of glycocalyx and it is tightly attached to the cell so that's what makes it different from being a slime they are both glycocalyx however they are a little bit different in terms of their structure so now let's talk about what are the functions of a slime or a capsule layer what are the functions of the glycocalyx so first the glycocalyx is there to prevent dehydration and nutrient loss so to protect bacteria from drying out and to protect it from losing or not getting enough nutrients it functions as an adherence factor

meaning it's sticky and it helps bacteria to adhere to surfaces this can allow it to produce what's called a biofilm and when bacteria are arranged in a biofilm which we'll talk more about in a minute it's this complex intermicrobial community when bacteria are in these biofilms antibiotics are up to a thousand times less likely to work if bacteria form a biofilm so it gives bacteria a major advantage to be resistant to antibiotics and to disinfectants and so forming this biofilm is protective for the bacteria protects bacteria from phagocytosis again bacillus anthracis is going to produce

a capsule of that d-glutamic acid and as a result one either it the white blood cells the phagocytes are not able to do phagocytosis or if they do phagocytosis they're not able to digest it because the immune system does not recognize that d glutamic acid and then lastly we have that it's a virulence factor and what that means is it has the ability to cause disease so an example of this would be streptococcus pneumoniae there are different strains of streptococcus pneumoniae and when we talk about genetics we'll talk about a process referred to as transformation

and what you'll see is that bacteria that produce a capsule are able to cause disease in mice meaning they're able to cause the mice to die of pneumonia but the same bacteria the streptococcus pneumoniae that does not produce the capsule does not cause disease and the mouse would survive and so this capsule or this glycocalyx is a virulence factor it has the ability to cause disease and so again down here this picture is an example of a capsule stain which we looked at right the background is stained with the congo red because congo red is

a negative stain and the negative stain is repelled by the negatively charged cell and this cell in the middle is stained with the safranin because safranin is a basic stain the basic stain has a positive charge and therefore it's attracted to the negatively charged cell and the capsule ends up being the colorless part right so this white part here is the capsule and so these are just the functions of this glycocalyx now again bacteria that can produce this capsule or this slime can lead to what is referred to as a biofilm and again a biofilm

is a complex inter-microbial community that's living in slime and so what you have is you have some surface and that surface might have some sort of organic surface coating so teeth for example can form a biofilm and what happens is is that you need these first colonists to come along and these first colonists are able to produce that glycocalyx they're able to produce that capsule or that slime and it allows them to stick to for example the surface of the teeth and so the bacteria will adhere they'll stick to the surface of the teeth and

that will recruit more bacteria to the biofilm and so those bacteria are going to send out basically these chemical signals that are going to attract other bacteria to this slime and what you're going to end up with is this complex intermicrobial community that's all living together in slime and that slime is protecting them from antibiotics from disinfectants etc and so they're all living in the slime and they are protected so if you've ever you know gone to bed at night without brushing your teeth and you know how you wake up in the morning and you

can feel that slime on your teeth your teeth feel real slimy that slime is a biofilm forming and that biofilm is formed by a type of bacteria called streptococcus mutans which is in your mouth and if you don't brush your teeth and that bacteria stays on the teeth it's going to produce that slime and it's going to lead to a biofilm on the teeth and when it does that by the time you can feel it by the time you can feel that kind of slimy feeling on your teeth typically the layer of biofilm is about

500 cells deep so think about that for a minute when you think about your teeth being slimy in the morning that is about 500 cells deep if you can feel that slime on your teeth that's pretty nasty so biofilms again intermicrobial communities and they form these pillar-like structures and these pillar-like structures give bacteria an advantage that it allows the bacteria to get more oxygen and to get more nutrients because you can imagine if this was just one solid layer right if this was just one solid layer all across only the bacteria that's exposed to the

outside would get access to oxygen and to nutrients etc but by forming these pillar-like structures we are now increasing the surface area to volume ratio meaning we have a lot more surface area so that the bacteria are more likely to be able to get oxygen and to be able to get the nutrients that they need and so by forming these pillar-like structures it gives bacteria an advantage now these biofilms can form the slime or hydrogels and then bacteria are attracted by chemicals via something called quorum sensing basically cells that are in the biofilm will send

out a chemical signal that will attract other bacteria to the biofilm this is a type of cell cell signaling and so now drugs are being developed to inhibit quorum sensing to inhibit bacteria from talking to one another to try and prevent biofilms from forming because again once a biofilm forms they're much more difficult to get rid of and so we want to prevent additional bacteria from getting to the biofilm so where can we find biofilms in the body one place would be the teeth so again like for streptococcus mutans it would be found in the

teeth and it causes that slime that we feel on our teeth mucous membranes so here is a biofilm that is forming on cilia along the mucous membranes so biofilms will form along mucous membranes heart valves catheters basically anytime you take something foreign from outside the body and put it in you run a risk of biofilms forming and so a catheter for example if we talked about a urinary catheter for example that is putting a tube up into the bladder for people that can't control their bladder and so that catheter that tubing runs a risk of

a biofilm forming implants whether it be breast implants or joint implants organ transplants basically anything that's coming from the outside in runs a risk of a biofilm so now let's talk about what advantage do bacteria get by forming a biofilm what is the advantage to the bacteria by forming a biofilm so one is it allows bacteria to share nutrients right because again it's this inter microbial community living together they can share nutrients they can do resource partitioning and divide up resources so that multiple bacteria can survive etc it can shelter bacteria from harmful factors in

the environment like desiccation or drying out right it helps them to retain water it helps them to be protected against antibiotics so again microbes are about a thousand times more resistant if they're in a biofilm than if they're not so it gives them a major advantage in being antibiotic resistant and it also helps protect them against the body's immune system because again if you have this thick layer of slime it's going to be a lot more difficult to do phagocytosis and to basically grab a hold of all the bacteria that's causing the infection and so

it also helps protect bacteria from the body's immune system and lastly it helps with what's called conjugation and that is the transfer of dna from one bacteria to another so because bacteria are living in close proximity it helps facilitate the transfer of dna from one cell to another and we will talk about conjugation in a little bit when we talk about pili which are the structures responsible for conjugation but bacteria living in a biofilm those bacteria are going to be more likely to be able to do conjugation because again they're living in close proximity so

now let's look at some bacteria that have capsules and so the first one that we can talk about is streptococcus pneumoniae you can guess by the name what disease it causes and it causes pneumonia next we have club ciel and pneumoniae and klebsiella ammonia is another bacteria that causes pneumonia it is a gram-negative raw bacteria that is typically going to be found in the gut however if it gets out of the gut and it gets into the lungs it can cause pneumonia or if it gets into the bladder it causes a urinary tract infection or

uti and so this is a normal bacteria that's part of normal flora in the gut but it becomes problematic if it gets out of the gut next we have hemophilus influenzae this is a type of bacteria notice the name says influenzae and you might think well it causes influenza it actually doesn't influenza is caused by a virus this is a type of bacteria and this is going to cause meningitis which is an inflammation of the meninges which is part of the nervous system so it causes meningitis or pneumonia we have pseudomonas ruginosa this is a

common cause of death in burn victims so in burn victims if this bacteria happens to get into the wound it can cause an infection which can be fatal pseudomonas is extremely resistant to not only antibiotics but also disinfectants as well and there have been instances of pseudomonas actually growing in lysol so not only is it not effective but it actually grew within the lysol and then when they used it to clean surfaces it ended up basically just putting pseudomonas all over a hospital setting and so pseudomonas is extremely resistant to antibiotics and disinfectants so we

have pseudomonas aeruginosa causes the infection and burn victims you'll also see later on we'll talk about pseudomonas again when we talk about we'll talk about how it can cause an infection in patients who have cystic fibrosis cystic fibrosis is a genetic condition in which people are born with it and they have defective chloride channels and as a result of having defective chloride channels they don't move water properly and they get this thick secretion in their lungs and when that secretion sits there if bacteria and specifically pseudomonas gets into those secretions and it sits there it

can cause an infection and it can kill these patients who have cystic fibrosis and so if you've ever seen the movie a fault in their stars and it's about patients who have cystic fibrosis and patients who have cf are told not to date other people who have cf and the reason is is that they're more likely to transmit this infection and then it ends up being fatal to both people because neither one can fight off the infection next we have neisseria meningitidis i know that looks like it's probably a typo for meningitis it's not the

bacterial name is meningitidis and neisseria gonorrhoeae now again it's different than gonorrhea spelling notice in the middle here the way i remember this one it has a hoe in the middle gonorrhea is a sexually transmitted infection so it's a sexually transmitted infection so if you're a hoe you could end up with gonorrhea now with gonorrhea that typically had been a sexually transmitted infection that used to be fairly easy to treat you would take an antibiotic and it would go away the problem is is that many strains of nasseria gonorrhea are now resistant to antibiotics and

there are multi-drug resistant strains meaning they're resistant to multiple drugs and so those strains of gonorrhea are becoming more and more difficult to treat and what once was very easy to treat is now becoming a lot more difficult in the case of neisseria meningitidis right that is that's going to cause meningitis which is an inflammation in the menin it's a type of bacteria that is only hosted by humans meaning it only infects people and it's the leading cause of bacterial meningitis in the united states and it's transmitted through saliva and if you happen to contract

nicer meningitis it can be quite fatal and in fact very very quickly there was a girl that went to my high school who contracted it and she basically you know one day went home she had flu like symptoms she wasn't feeling well she went to bed woke up the next morning she had bruises all over her body her mom rushed her to the er and she died that very next day so within 24 hours she had died from this form of meningitis and so this can be quite fatal and so at our school we all

got notified you know if you shared drinks with her or you had kissed her that you should go get tested to see if you happen to also carry nyseria meningitis meaning you became infected with it because it can be quite fatal if you contract that form of meningitis next we have cryptococcus neoformans this is a yeast it is a fungus so instead of being bacterial this is actually a yeast and this causes what's called cryptococcosis and this is basically this organism can be found in bird droppings and if for example if somebody has an immune

um they are immunocompromised their immune system is not functioning properly like is the case for patients who have aids which is late stage hiv um if they happen to have a compromised immune system and they leave their windows open and a bird drop bird dropping happens like the bird poops and it happens to get into your lungs then it can cause in serious infections for aids patients and can be fatal and so again if your immune system is functioning normally you're not quite as at risk for this however if you have some condition that compromises

your immune system like aids this could be very fatal and so these are just some different examples of different organisms that have a capsule they have this glycocalyx and they can cause disease so question for you which of the following statements about the bacterial glycocalyx is false red it may be involved in the formation of biofilms yellow it is used to adhere to surfaces green it makes bacteria non-pathogenic blue it protects from dehydration and nutrient loss or purple it may be composed of polysaccharide so what i want you to do is to pause your video

think about your answer and when you're ready go ahead and push play to hear the answer so if you said green you would be correct so green is the statement that's false glycocalyx is involved in the formation of biofilms that is true it is used to adhere to surfaces that's true because it's sticky blue it protects from dehydration and nutrient loss that is true purple it may be composed of polysaccharide that is true it could also be composed of polypeptide like for bacillus anthracis that's true but it does not make bacteria non-pathogenic instead it makes

bacteria pathogenic meaning it makes bacteria able to cause disease and so green is the statement that is false so in addition to glycocalyx some bacteria might have what's called an s layer and an s layer is a single layer of thousands of copies of a single protein that are linked together like a chain male and this is only produced when bacteria are in a hostile environment and so what you're going to notice is if you look at this diagram here here is that peptidoglycan then you can see this thin layer of s layer and then

external to that would be the glycocalyx and so this s layer is only produced when bacteria are in a hostile environment so next we're going to move on and we are going to talk about motility structures in bacteria basically structures that allow bacteria to move so the main structure used for motility is going to be a flagellum and in a prokaryotic flagellum it has three parts it has a filament a hook and a basal body the filament is the tail-like extension that's the part that comes out from the cell it is going to contain the

globular protein flagellin which is arranged in several chains that intertwine and form a helix around a hollow core when we look at eukaryotic flagellum you will start to see how they are different than prokaryotic flagellum eukaryotic flagellum is made of a protein called tubulin prokaryotic flagellum is made of a protein called flagellin next we have the hook and the hook is basically the part that is going to rotate it's going to move to help move flagella again one of the differences between prokaryotic and eukaryotic in prokaryotic bacteria the way that the flagellum moves is that

the hook rotates in a circular motion and that causes the tail the fl the filament think of it kind of like a propeller in a helicopter for example it's going to go in a circular motion that is very different than eukaryotic flagellum you will learn later on that eukaryotic flagellum moves in an undulating or wave-like motion so the way that they move is a little bit different as well in the case of prokaryotic cells they have this hook and the hook circles in a circle and it's going to cause the filament to move in a

circular motion like a propeller then we have the basal body and the basal body is used to anchor the flagellum into the cell wall and the plasma membrane and the structure of the basal body can be different between gram-negative and gram-positive and that has to do with the composition of the cell wall so if you recall when we talked about our gram stain our outer membrane is in gram-negative so it has this outer membrane and it has a thin layer of peptidoglycan in the case of gram-positive right gram-positive have a cell membrane they have a

thick layer of peptidoglycan and they have no outer membrane they just have the one membrane so as a result the way that i remember this is that basically there are two rings two rings within the basal body the part that anchors the flagellum into the cell envelope in gram-positive there are only two rings because there's only one membrane in the case of gram-negative we have two membranes so we have four rings in terms of the basal body so the way i remember it it's not necessarily that that's the way it's set up within the cell

envelope but the way that i remember this is that for each membrane that they have there will be two rings so gram-positive only have one cell membrane they will have two rings in terms of their basal body gram-negative have two membranes so instead of having two rings they have four rings to help anchor it into the cell envelope the cell envelope is referring to the cell membrane and the cell wall together that whole structure is going to be your cell envelope and so this is your structure of a prokaryotic flagellum now in terms of the

number of flagellum there are different terms depending on the way that the flagella are arranged if we say that the cell is atricus a means without so no flagellum this would be a bacteria that does not have flagellum and oftentimes means that they are non-modal if they have one we say that they're monotrichus mono means one at one end so this picture here is an example of a bacterium that is monotrichus if we say that it's lophotricus the where remember lofatricus i think lumped together there are more than one at just one end so there's

a lump or there's a cluster of multiple flagella at one end so that's lofotercus so multiple flagella at one end if we say that it's amphitricus you're going to see when we talk about the cell membrane we talk about that a phospholipid is amphipathic the phospholipid itself is going to be ampatricus meaning it has a dual nature it has you know the hydrophilic head and it has the hydrophobic tail so amphi means like both ends so amputricus means that we have flagella coming out of both ends so we have one here we have one here

if we say that it is peritricus peritricus means that it's over the entire cell so there are flagellum just coming off everywhere all over the cell so e coli for example would be peritricus it has lots and lots of flagella on its surface now again the way in which the bacterium is going to move is going to be different than that of how a eukaryotic cell would move and so for bacterial flagellum if they move if they move their flagellum in a counterclockwise motion that's going to cause the bacteria to do what we call a

run meaning it's going to move in a directed fashion if however the flagellum starts to rotate the other way and it starts to rotate in a clockwise manner that is going to cause the bacteria to tumble and what that means is it's going to change direction and then it's going to go back and it's going to rotate it counterclockwise and it's going to do a run and then it's going to go back and turn it the other way it's going to do it counterclockwise and it's going to do a tumble and so this is going

to continually happen with the bacterium that causes it to move so if we talk about the way that bacteria move so if there are no attractants or no repellents there are no s stimuli present bacteria are going to move in a very random fashion they're going to alternate between runs and tumbles so the green are the runs the reds are the tumbles so notice that this bacteria is not going anywhere in particular however if there is some sort of attractant concentration maybe it's a chemical stimulus like food and bacteria are trying to move towards that

food notice that you get this net movement towards the attractant it's not a straight line it's not going to be perfect but bacteria will start to move towards the that signal and so if your stimulus is a chemical stimulus we call that chemotaxis chemo refers to chemical that is movement in response to a chemical now when we talk about movement in response to a chemical we can talk about positive chemotaxis and negative chemotaxis positive means motility towards a stimulus so like food for example bacteria would display positive chemotaxis towards that food source it's going to

move towards that food if we say that it's negative chemotaxis that is motility away from the stimulus meaning the bacteria wants to go away from it it could be a toxin it could be a waste product etc but bacteria want to move away from that stimulus now stimuli could also not just be chemical but it could be light phototaxis photo refers to light that is movement in response to light so like a plant for example would display positive phototaxes it's going to grow towards sunlight because they need sunlight to do photosynthesis so that would be

positive phototaxes now if we talk about the way in which bacteria move they move again using flagella flagellar proteins are what are called h antigens and h antigens are useful to determine strains of a bacteria what is an antigen well an antigen is any substance that elicits an immune response meaning it's something that the immune system recognizes as foreign so if we look at these h antigens these different types of antigens that can be present on the flagella if we look at those h antigens we can in some cases determine the strain of bacteria that

we're looking at for example everybody has e coli in your gut it's part of your normal flora that e coli that's in your gut isn't going to cause disease however you've probably heard of e coli causing food poisoning if you think of chipotle for example they've had outbreaks of e coli it's not the standard e coli that's found in your gut it's a particular strain of e coli and that strain of e coli is called o157 h7 so it has this o antigen which you're going to learn later is part of its lps so part

of its outer membrane it has that type of antigen and it also has this h7 or flagellar antigen this special molecule that's found on the flagella and so that particular strain of e coli is identified by these two antigens this o antigen and this h antigen and this strain of e coli is the one that's going to make you sick and that's because that strain of e coli has acquired the gene for what's called a shiga toxin and shigella is a type of bacteria that produces this shiga toxin and it causes patients to have severe

diarrheal disease and upset stomach etc now e coli at some point hooked up with shigella and shigella passed the gene for the shiga toxin to e coli e coli now has this gene it has this dna sequence and it now produces that shiga toxin protein and that strain of e coli is the one that's going to cause you to get food poisoning it's not your standard e coli because the standard e coli are not going to produce that toxin but this e coli o157 h7 is going to produce this toxin and therefore when you consume

this one that is going to give you food poisoning and so the h antigen is just this type of foreign molecule on the flagella that help us to identify this particular strain of e coli now we can also talk about flagella being attached to the outside of the cell and if it's attached to the outside of the cell it's referred to as an endoflagella endo meaning within it's attached to the outside of the cell that's also referred to referred to as an axial filament and axial filament is is a flagella that is anchored at one

end and then it wraps around the length of the bacterium this type of structure is found in spirochetes right remember that spirochetes are our flexible spirals and when we talked about our negative stain and we talked about using a negative stain to look for spirochetes right you can think of several diseases that were caused by spirochetes one of which being treponema pallidum causes syphilis entreponemia pallidum remember is a sexually transmitted infection it's going to be passed from person to person through sexual contact and so if somebody is infected and they have this canker the sore

and you happen to come in contact with that and it passes from the genitals of one person who has it to somebody else that they're having a sexual contact with this axial filament is going to help the spirochete to move like a corkscrew so it's going to work just like a corkscrew would if you're trying to open a bottle of wine it's going to screw its way through so if you screw you get screwed very funny right sexually transmitted infection so it's going to screw its way through the skin it's going to penetrate it's going

to cause a canker at the site of where the bacteria has gone in and it's then going to lead to syphilis in the person who made contact another example of this the one that's shown here leptospira leptospira is found in infected animal urine like cats and dogs etc and if let's say a cat urinates in a lake you can end up with something called leptospirosis where you can get an unexplained fever and you get really sick if left untreated and so this would just be another example of an organism that would have an axial filament

it's actually the flagella in this case is wrapped around the length of the spirochete it's not free like a typical flagellum would be so next we have our fimbriae fimbriae are these fine proteinaceous meaning protein containing hair like bristles from the surface of the cell and these structures are shorter meaning they're not as long they are more straight and they are thinner than flagella and their purpose is different than flagella flagella is used for motility for movement fimbriae is not fimbriae is used for attachment so it allows tight adhesion between fimbriae and epithelial cells and

this allows bacteria to colonize and infect host tissues so what you're looking at down here this is intestinal microvilli these little projections along the intestines and e coli is a type of bacteria that produces fimbriae and these structures these protein structures allow it to attach and adhere to the intestinal microvilli it allows it to attach to the intestinal wall and it allows e coli to live and colonize the gut and so fimbriae is a structure again not all bacteria have them but those that do have them that structure is used for attachment it allows bacteria

to adhere to a surface next we have pili or pilis would be singular this is a rigid tubular structure made of this pillin protein and this is found in gram-negative cells so this is going to be found in gram-negative cells exclusively and it has several purposes it has several uses so one main thing that pillai do is that they're used to transfer genetic material through what's called conjugation and that is that one cell is going to produce these pillai and it's gonna send out these extensions to another cell and they're gonna hook up and the

one that sent this projection the one that produced the pili can then transfer genes to this recipient and those genes could be genes for antibiotic resistance so that's how bacteria can acquire antibiotic resistance it could pass genes for the production of a capsule for bacteria to produce fimbriae for bacteria to produce pili to produce toxins etc basically it's a way for bacteria to hook up and exchange genetic information one bacteria is going to give genes give dna sequences to a recipient that is referred to as conjugation it can also act like fembriae and assist in

attachment and it can act like flagella and also help to make bacteria modal it does this gliding and twitching motion instead so pillai actually do a lot of different things they have a lot of purposes within the cell but the one that we think of most commonly is conjugation so allowing bacteria to hook up and to exchange genetic information and you'll see a lot more about this in our genetics chapter so question for you which of the following is not part of a flagella red filament yellow hook green fimbriae blue basal body so i want

you to think about your answer pause your video and when you're ready push play to hear the answer if you said green fimbriae you are correct the fimbriae is not part of the flagellum it's a totally separate structure right it's used for attachment it is shorter it's thinner it's more rigid it's not like a bacterium flagellum so the filament again is the part that's coming off for the flagellum it's the tail like extension the hook is the part that rotates and the basal body is the part of the flagellum that anchors it into the cell

envelope so the fembriae is not part of the flagellum so now we're going to move to structures inside the cell wall of prokaryotes so if we move inside we have the cytoplasm this is the substance inside the plasma membrane and it's approximately 80 percent water plus proteins carbohydrates lipids ions etc and the purpose of the cytoplasm is that it serves as a pool for building blocks for cell synthesis or for sources of energy so basically for cells to make different structures within the cell serves as a pool to make you know macromolecules when the cell

needs to divide etc and so that fluid inside the cell membrane is the cytoplasm and within the cytoplasm it has this semi-fluid substance that we call cytosol now bacteria have a nucleoid region nucleoid region so it's not a nucleus it is not surrounded by a membrane but it's just this region within the cell where the dna is found and if we look at types of dna sequences that would be found in the nucleoid region we can have bacterial chromosomes and the bacterial chromosomes again are typically one circular double-stranded chromosome or dna now again some bacteria

might have more than one but typically most bacterial chromosomes are one circular double-stranded dna and the bacterial chromosome is going to carry so you should put this as a note here it's going to carry essential genes meaning that piece of dna makes proteins that are absolutely necessary for the cell so when we talk about metabolism for example and we talk about bacteria doing glycolysis an enzyme in glycolysis is going to be essential bacteria need it to carry out that process that gene would be on a bacterial chromosome that is an essential gene plasmids on the

other hand are small extra chromosomal genetic elements meaning that they're not part of the host chromosome they are separate circular dnas and the purpose of the plasmid is that it's going to carry non-crucial genes basically it's going to carry dna sequences that give bacteria an advantage but aren't necessarily necessary so a gene for antibiotic resistance might be found on a plasmid because bacteria don't necessarily require it but it is helpful if they have it production of a toxin for example would be on a plasmid and so the difference between a plasmid and a chromosome again

not only are they you know essential genes for the chromosome and non-essential genes for plasmids but the other big thing is is that bacteria will only replicate their chromosome when they are going to divide plasmas are separate they can replicate independently of cell division so they have some autonomy in terms of the way that they replicate and so different plasmids have different what we call copy numbers or basically how fast they replicate and they produce copies of themselves so a plasmid is going to be extra chromosomal and it gives bacteria advantage and it replicates on

its own so now we're going to look at the prokaryotic ribosome and the prokaryotic ribosome remember that all cells have ribosomes prokaryotic ribosomes are used for protein synthesis so again it's how the cell is going to synthesize or produce proteins the ribosome is made of ribosomal rna and proteins so it's a mixture it's proteins and ribosomal rna and ribosomal rna is basically just a type of rna and in the case of the ribosome the ribosomal rna plays a role in formation of peptide bonds meaning it plays a role in the formation of the protein it

helps with the synthesis and the catalyst to form a protein and so this is not a membrane-bound organelle it's not made of a membrane it's simply a collection of ribosomal rna and proteins and so this is why prokaryotic cells have it right because prokaryotic cells don't have membrane-bound organelles but they do have a ribosome it's not a membrane-bound structure now prokaryotic ribosomes there are two subunits there is what is called the small subunit so here's your small subunit and in prokaryotic cells the small subunit is what we call 30s the s just refers to this

spheberg unit it basically has to do with how it centrifuges like if you put it in a tube and you put it in a sucrose gradient how fast that ribosomal subunit is going to move through a tube as it's being centrifuged which means to spin it really fast and so basically the small subunit is made of what we call a 30s the large subunit is what we call a 50s however collectively when you put the two subunits together they actually make a 70s ribosome it's not necessarily additive so the two subunits together will measure at

70s and we call these 70s ribosomes this is going to be different for eukaryotic ribosomes eukaryotic ribosomes the small subunit is going to be 40s so in a eukaryotic cell it's going to be 40s in a eukaryotic cell the large is going to be a 60s so a 40 and a 60 and combined they weigh 80s so i know that's a little bit tricky you're just going to have to study those numbers to just know it's a 30s and a 50s and combined it gives you a 70s when we look at eukaryotic ribosomes it's going

to be different it's a 60s and a 40s and combined they are ads so next we have our inclusions and our inclusions are these intracellular storage bodies that serve as temporary reserve deposits basically it's where the cell is going to store something so if we look at metachromatic granules or volutin this is basically a place for phosphate reserves the cell uses phosphates to make atp so adenosine triphosphate which is energy it's used to make phospholipids and it's used to make nucleic acids like dna and rna and so this is basically where bacteria can store their

phosphate reserves bacteria can have polysaccharide granules their function is energy reserves you can imagine what those study those store those store polysaccharides those store sugars we can have lipid inclusions again those are energy reserves because lipids are rich in energy we have sulfur granules those also serve as energy reserves we have carboxysome those basically will store an enzyme called rubisco and this rubisco enzyme is used in carbon dioxide fixation during photosynthesis so basically it's going to take it's going to play a role in photosynthesis so cyanobacteria for example would have these carboxysomes to store that

rubisco enzyme which allows them to do photosynthesis bacteria may have what are called gas vacuoles these are basically protein covered cylinders that maintain buoyancy meaning it helps bacteria to float now think about why certain bacteria might want to float and the answer is again cyanobacteria which does photosynthesis is aquatic if that bacteria were to sink to the bottom is it going to get access to sunlight and the answer is no it's not going to have access to sunlight and therefore is not going to be able to do photosynthesis however if they have gas in these

vacuoles and they float right if they go to the surface they're going to get access to the sunlight and they're going to be able to do photosynthesis and so these gas vacuoles basically help bacteria float bacteria can have magnetosums and these are basically these iron oxide inclusions and they're used to help destroy hydrogen peroxide which can be toxic to the cell and so this is just showing you an electron micrograph of these magnetosomes they are artificially colored pink and so you can see these little inclusions within the cell and they are basically going to act

as these inclusions and so lastly we're going to look at an endospore and an endospore is found mostly in gram positive so again not exclusively but mostly gram positive and there are two main genre that produce endospores and that is clostridium and bacillus clostridium is going to be our anaerobic meaning it grows in the absence of oxygen bacillus is aerobic it grows in the presence of oxygen so endospores are basically a structure that are used for survival they're used to survive adverse environments so when conditions become unfavorable you can think of an endospore just like

in the endospore stain when i talk about this you can think of an endospore as a structure that bacteria can produce that basically allow them to go into hibernation it's when they experience their conditions as being harsh what are some harsh conditions dehydration so not having enough water lack of nutrients radiation like uv for example heat freezing chemicals etc lack of o2 in some cases or presence of o2 in some cases but basically when the bacteria experience their environment as harsh they will package their dna into this keratin structure this endospore is made of keratin

and so it's this tough structural protein and it's going to form around the dna and it's going to protect that dna so as the bacteria form their endospore that process for the formation of the endospore is referred to as sporulation so that's the process of forming the endospore when conditions become favorable again it's going to go back to being a vegetative state and that process going from a spore to a vegetative state again that process is referred to as germination think of a plant can germinate when the seed sprouts that's germination it's like it's coming

out same idea in the case of the endospores it's like the endospore is coming out it's going back to a metabolically active state it's no longer going to be in hibernation now in terms of the endospores their longevity verges on immortality so anywhere from 25 to 250 million years so these endospores have been found to have been millions of years old and they're able to basically go back to being vegetative cells so you can almost think of it kind of like zombie bacteria they're bacteria that basically can shut themselves down they can go into hibernation

and then when conditions become favorable then they can go back to being metabolically active and reproducing and so this is just showing you an endospore in bacillus anthracis so it's starting to form the structure within the cell and it's basically going to wait it out until conditions become favorable so again this is a similar drawing that was seen in your lab for the endospore and so again we have our vegetative cell this cell is metabolically active when conditions become harsh they're going to undergo sporulation they're going to package up their dna and they're going to

put it in this endospore structure which is made of keratin and that endospore can be terminal meaning off to one end it could be centrally located in the middle it could be subterminal which means not all the way to the end but off to one side and so while that spore is still within the cell it's referred to as an endospore and the endospore is within the vegetative mother cell now if this cell still is experiencing their condition as being harsh eventually this vegetative mother cell is going to break down and you're going to be

left with a spore now this is not to be confused with a spore like for fungi for example in fungi when we talk about spores or implants when we talk about spores those are structures that are used for reproduction meaning that's how the cell is going to reproduce in bacteria spores are not for reproduction in fact it's quite the opposite it's when the cell is not dividing so be careful a spore in bacteria is not a reproductive structure it's the opposite it's when it's dormant it's when it's not metabolically active and it's not dividing however

when conditions become favorable bacteria can germinate and they can go back to being a metabolically active vegetative cell so it usually takes about six to ten hours for sporulation to occur this will take several steps germination typically only takes about one and a half hours and that's how quickly it can go back to being metabolically active and so this is how endospores are formed again not all bacteria will have this structure this is typically gram-positive and most commonly in bacillus and clostridium so this is just showing you some examples of endospore producing bacteria and the

diseases that they cause so the first one is bacillus anthracis this bacteria is found in soil as well as infected animals cows for example can transmit bacillus anthraces etc this if it's bacillus it is aerobic right so it's going to grow in the presence of oxygen and it causes the disease anthrax it could be cutaneous which is on the skin it could be in the lungs but think about the lungs and the skin those are both environments where oxygen is readily available so that's how one of the ways you can know that bacillus anthracis must

be aerobic because it grows where oxygen is present next we have clostridium botulinum clostridium botulinum can be found in soil and canned foods and this bacteria is anaerobic grows in the absence of oxygen and the disease that it causes is botulism botulism can be can happen in infants one of the ways that infants can contract botulin botulism is through consumption of honey this is why infants are parents are told don't feed infants honey until they're over a year because before a year their immune system is not able to fight it off and they could get

botulism which leads to this floppy baby syndrome where their muscle tone is just really low um and they don't um they're not able to have like their muscles contract properly uh botulism is also associated with canned foods if you've ever see like heard people say you know don't eat from a can that's severely dented especially if it's along the seam of the can and the reason for that is that if the can gets dented and it gets these little microscopic holes in the can and this bacteria gets in it can also cause this botulism clostridium

botulinum produces this botulinum toxin which is one of the most powerful neurotoxins known to mankind and this toxin basically causes muscles to not contract it causes muscles to be relaxed and so in this case botulinum toxin is used in botox so if you've ever heard of botox right botox is an injection and it's where they inject this botulinum toxin into basically the nerves the muscles and they basically get the muscles to relax so it basically softens the wrinkles and so when you think of botox that's probably you know the most common use you think of

botox is for you know wrinkles however botox does have a lot of other uses that are actually very important they can be used in it can be used for urinary incontinence so people who have like an overactive bladder botulinum toxin can be injected to help relax the bladder so it's not anymore and it's not causing the overactive bladder uh botox can be used for migraines for example there are actually many other uses for botox other than you know wrinkles it does have other uses as well and so this is actually produced by allergan which has

now been bought by another company but allergan is a company that is in irvine it's local and that is where botox is produced so that's clustered in botulinum clostridium perfringens clostridium perfringens is found in soil and in deep wounds it's an anaerobic bacteria and it causes gas gangrene basically it causes the tissue to become necrotic and it starts to rot and as the tissue starts to become necrotic and as it starts to rot and there's not blood flow well now that is an anaerobic environment and clostridium perfringens can grow and so one of the things

that or one of the problems is that when bacteria are in endospores they're very they're very resistant to antibiotics and so one of the things that can be done for gangrene is that medical maggots can be put on the tissue and those maggots can consume the endospores and try to get them out of the tissue but if not possible oftentimes what has to happen is going to be amputation because once that tissue is necrotic and it's dead oftentimes it needs to be removed we have clostridium tetani which is found in soil as well as deep

wounds it is anaerobic and it's going to cause tetanus tetanus you can think of kind of like the opposite of botulism botulism is where the muscle tone um is going to be very relaxed and that's when it leads to that floppy baby syndrome tetanus is the opposite it causes the muscles to contract and they get stuck in this contract form and the patients get you know a lock jaw they get these muscle contortions where their body is like frozen in this crazy contortion because of this uh tetanus toxin and so that is produced by clostridium

tetani and then lastly we have clostridium difficile what you'll often hear referred to as c diff and c diff is transmitted through feces and through infected patients it is one of the top five killers of hospital-acquired infections meaning you go into the hospital for something else and you leave with a c diff infection because it's highly contagious and it's really difficult to treat it is a bacteria that is anaerobic and it causes colitis basically it's going to cause this inflammation in the colon and it's going to basically give the patient uncontrollable diarrhea and so the

patient just gets really sick with this just really awful diarrheal disease and basically when this patient has diarrhea millions or billions of endospores are being released and then a healthcare worker can take those endospores or that disease to other patients and that's how you end up with this hospital-acquired infection because they produce lots and lots of these endospores in the feces of people who have c diff and so one of the ways that they now try and treat c diff because c diff is not well managed often with antibiotics it's really difficult to get rid

of it so one of the things that they sometimes will do is what's called a fecal transplant and what they will do is they'll take fecal matter from somebody else and they will transplant it into somebody who has a c diff infection oftentimes it would be somebody that you live with that you have a lot of contact with because that person would be likely to have a lot of the same normal flora bacteria in their gut and so when they do a fecal transplant the goal is basically by putting that fecal matter back into the

intestines so put somebody else's fecal matter into the intestines the idea is to put good bacteria back into the gut so that it can out compete the c diff and so there has been some success with this approach by basically putting back in good bacteria to out-compete the bad bacteria to out-compete the c diff for the infection in the intestine and so this is just kind of a list of some examples of endospore producing bacteria and the disease that they cause so question for you what structure protects pathogenic bacteria from phagocytosis is it red capsule

yellow endospore green flagellum blue axial filament or purple ribosomes so take a minute pause your video think about your answer and when you're ready push play to hear the answer so if you said capsule you are correct the capsule is a structure that is used to protect against phagocytosis it's going to protect from the immune system from being able to engulf that bacteria the endospore is not going to protect against phagocytosis basically an endospore is the structure that bacteria produce in response to a harsh condition it's not necessarily going to protect against phagocytosis flagellum green

is not correct that is a structure used for motility axial filaments is also a structure used for motility again that's an endofilament it's what's used for motility for spirochetes ribosomes are not going to be used to protect from phagocytosis the ribosomes job is to basically synthesize protein so the capsule is the structure that's going to protect against phagocytosis and so the next part is going to be looking at bacterial cell walls the cell wall is going to be just outside the cell membrane and the function of the cell wall is to prevent what's called osmotic

lysis meaning that to prevent if water goes into the bacterial cell to prevent the bacteria from lysing or breaking open and so we'll get to that topic in just another minute the other function of the cell wall is that it's there to help protect the cell membrane and remember that when we looked at bacteria most bacterial cell walls are made primarily of peptidoglycan again peptido refers to protein glycan refers to sugar and so you're going to see when we look at the peptidoglycan that it's a mixture of these sugars and these proteins put together and

so the cell wall often contributes to the pathogenesity which is basically the ability for the bacteria to cause disease and so if we look at peptidoglycan peptidoglycan is a polymer of a disaccharide so meaning that it's this disaccharide dye means two sugars put together and they're going to be repeating over and over again in the peptidoglycan and if we look at the peptidoglycan the disaccharide is made of what's called nag and nam and so this is the sugar for nag this is the sugar for nam and so i'm not gonna ask you what nag and

nam stand for okay but if you wanted to look at it it's n acetyl glucosamine and then nam would be the n acetyl muramic acid and so when we look at these peptidoglycan the disaccharide that's used is naga nam bound together so now elaborating on the fact that the peptidoglycan is nag and nam in addition we need to look at the overall structure and so when we look at this notice we have alternating nag nam nag nam and so we get these rows or these backbones of carbohydrates this backbone of carbohydrates those are going to

be typically about 10 to 65 sugars long for the carbohydrate backbone and running perpendicular to those carbohydrate backbones are the protein part of this and so again remember that when we look at peptidoglycan peptido refers to protein glycan is going to be the sugar and so when we look at the amino acids that are used they have these peptide cross bridges and so what you'll see is you'll see that it's these amino acids and these amino acids link the peptidoglycan the sugars together and so the amino acids attach to the nam so amino acids attach

to nam and those amino acids are alternating d and l amino acids and so remember that in nature most amino acids exist in nature as l amino acids but in this case we're actually looking at the isomers and they're going to alternate between the d and the l form of those amino acids and so again our rows of carbohydrates are linked together by polypeptides so now we're going to compare and contrast gram positive and gram negative bacterial cell walls and so if you remember back to lab where we looked at the cell walls for the

gram stain gram positives remember have a very thick layer of peptidoglycan and in that peptidoglycan there's what's called tachoic acids and these teichoic acids are going to consist of an alcohol and a phosphate and the tachoic acids are negatively charged and what that's used for is it helps to bind and regulate the movement of cations meaning positively charged ions into and out of the cell and when we look at teichoic acids there are two main categories there are the lipotechoic acids lipo refers to lipids and if you look here are the lipotechoic acids and those

actually help to link the cell wall into the cell membrane meaning that these types of tachoic acid can actually embed themselves in the lipid in the cell membrane there are also what are called wall tachoic acids and so if you look here are the wall tichoic acids and notice that they're not embedded in the cell membrane instead the wall tychoic acids are used to link those peptidoglycan layers together in addition the um cyclic acids can be antigenic and remember that when we looked at flagella for example flagella have an h antigen which can be useful

in identifying the bacteria same thing for the tachoic acids is that these have these antigens which are these molecules that can be regulated or identified by the immune system and using those antigens on the titanic acid it can help us to identify the bacteria in certain lab tests so when we look at gram-negative bacteria remember that for gram-negative bacteria it has a very thin layer of peptidoglycan but it has an outer membrane and so when we look at the structure of the gram-negative cell walls they don't have tickoic acids and so they lack the tachoic

acids because they have a thin layer of peptidoglycan the space that's in between the two membranes that's called the periplasmic space and so the periplasmic space is going to be between the outer membrane and the inner membrane and in the case of gram negatives it has the peptidoglycan when we look at the outer membrane of the gram-negative organisms the outer membrane has three parts and these three parts collectively are called lps or lipopolysaccharides and so when we look at these the lps has an o polysaccharide a core polysaccharide and lipid a and so in a

minute we'll talk more about what these lps are used for in addition they also have phospholipids so again they're those phospholipid bilayer and they have these lipoproteins which help to hold the outer membrane to the periplasmic space and again one of the things that's going to be different from gram-positive versus gram-negative is that for gram-negative cell walls no ticoic acid so they have an outer membrane they have thin peptidoglycan and they don't use tacoic acids in their cell wall so if we look at the outer membrane of gram-negative bacteria this has several functions one is

that this outer membrane helps to protect from phagocytosis remember that means that that is when the white blood cells engulf the bacteria and take them in and destroy them and so this membrane makes it harder for the immune system to do phagocytosis which then also then means it's harder for the body to eliminate that bacteria it also helps to protect gram-negative organisms from something called complement and complement you're going to learn about when we talk about immunology but these are basically blood defense proteins proteins that the immune system produces in response to some type of

infection and so this the outer membrane of gram-negative bacteria helps prevent against complement meaning again it helps it to survive in addition outer membrane is also used to protect the bacteria from antibiotics and one of the ways through which they can do that is embedded in this membrane are these porns and these porins are these channels through the membrane and these proteins these porins are selectively permeable and so what that means is that these porns can regulate what goes into and out of the cell and so as a result sometimes the porns get mutations through

which antibiotics no longer can get into the gram-negative cell and so having this outer membrane helps gram negative bacteria to be typically more resistant to antibiotics the outer membrane is also protective against digestive enzymes detergents etc and so you're gonna see that this is really important when we talk about why gram-negative organisms are so important so if we look now at more detail of the outer cell membrane we're going to focus more now on looking at in the outer membrane so again here's our outer membrane notice here's our periplasmic space again it's the space between

the cell membrane and the outer membrane we have our thin layer of peptidoglycan we have those lipoproteins that link the peptidoglycan into those membranes and then now we're going to focus on talking about the lipopolysaccharides the lps and so if we look at a bigger diagram of the lps again the parts of the lps is going to be what's called an op polysaccharide and so if we look this is an lps blown up here is the o polysaccharide and the o polysaccharide at the top so this would be up here the o polysaccharide the o

polysaccharide is the antigen again it's what allows to recognize and to determine a particular type of bacteria meaning it's useful for distinguishing between different species and so remember when i talked about e coli e coli is the type of bacteria found in your gut and remember we said that normal strains of e coli don't cause food poisoning the strains of e coli that typically are responsible for food poisoning is the e coli o157 h7 and we said h7 that's for the flagellar antigen the o157 is for the antigen that's found on the lps in the

outer membrane and again these antigens are useful for identifying a particular type of bacteria we also have this core polysaccharide so again poly meaning many sugars so these are these sugars linked together and the core polysaccharide is there to provide stability it's there for structural purposes and then lastly we have our lipid a and the lipid a helps the lps to embed in the cell membrane and lipid a also has what's called an endotoxin and an endotoxin is basically going to be a toxin that the bacteria produce and when they produce this endo endotoxin it

causes fever blood vessel damage blood pressure goes down so you start to lose blood out of the leaky blood vessels um that can lead to inappropriate blood clotting heart rate goes up and then shock and if left untreated this can prove to be fatal and so for the gram-negative organisms remember that we said that one of the main reasons that a physician would order a gram stain is because determining the gram reaction of the infection is extremely important remember we said that that's for two reasons one being that if you look at um the differences

between gram positives and gram negatives some antibiotics like penicillin for example penicillin inhibits peptidoglycan gram positives have a thick layer of peptidoglycan gram negatives have a thin layer so penicillin is specific towards gram-positive organisms so if your patient had a gram-negative infection giving them penicillin won't be useful to treat that infection but the other important reason about knowing the gram reaction is remember that i mentioned that if you if your patient has a gram-negative infection you don't want to prescribe an antibiotic that's going to cause the bacterial cells to rupture that's called bacteriocidal cytomeans kill

you don't want to prescribe a drug that's going to kill the gram-negative organism which would rupture the cell and it would release all that lipid a which could lead to shock so if your patient had a gram-negative infection you would instead want to prescribe a drug that is what we call bacteriostatic static means stays the same and for bacteriostatic antibiotics those antibiotics simply inhibit the bacteria from growing and they give the immune system time to catch up and so again knowing the type of infection that a patient has can be really important for trying to

decide what antibiotic to prescribe to that patient so this slide is just comparing gram positives and gram negatives so again gram positives have a thick peptidoglycan again it's about eight times thicker typically than gram negatives gram positives have the tichoic acids in their cell wall gram negatives have a thin peptidoglycan they lack teichoic acids they have an outer membrane so again if we look at this outer membrane right we have our cell membrane we have the outer membrane and we have this periplasmic space the space that exists between the outer membrane and the cell membrane

and so this is looking at comparing gram positives and gram negatives and so in your question set there's a question about to diagram what the cell walls look like for gram positive versus gram-negative and so these examples down here would be like what you'd want to draw so you would draw gram positives have a thick peptidoglycan they have the lipotincoic acids again those are the ones that link the peptidoglycan to the cell membrane they have wall tichoic acids which help to hold them together but they don't go into the cell membrane of the gram-negative organism

again when we look at gram positives you would want the cell membrane you would want the periplasmic space you would want to label a thin layer of peptidoglycan periplasmic space again and then the outer membrane and so when we look at the outer membrane it has those porins or the channels which regulate what goes into an out for a gram-negative organism and it has those lipopolysaccharides the lps and those have those three parts the o polysaccharide being at the top the core polysaccharide being here and then the lipid a is the part that's embedded in

the membrane so this is just another diagram showing you again comparing gram positives and gram negatives and so these are an elec electron micrograph and these have been artificially colored so these colors that you're seeing on this image don't actually exist when these pictures were taken but what these are what these are doing is that the yellow is where they've labeled the cell membrane and so remember that all cells have a cell membrane so in this case here's our cell membrane here's our cell membrane for our gram positives and our gram-negative if we look at

the peptidoglycan the peptidoglycan has been colored brown notice that the peptidoglycan is much thicker in the gram positives than it is in the gram negatives and again gram positives have a much thicker peptidoglycan when compared to gram negatives however gram negatives have this additional outer membrane and notice that it's lacking for the gram positives the other thing to point out is that notice that when we look over here notice you see this area that's in between the peptidoglycan and the outer membrane that's the periplasmic space and over here that's the periplasmic space it's the space

between the peptidoglycan and the membrane over here notice there seems to be a little gap here but it's typically not thought of as gram positives having a periplasmic space that perhaps this little gap that you're seeing there is simply due to an artifact that occurred during this procedure and so typically when we think of gram positives and gram negatives gram negatives have that periplasmic space because they have the cell membrane and the outer membrane gram positives on the other hand have the cell membrane and then they have the thick layer of peptidoglycan so remember in

lab we talked about the gram stain and the gram stand remember is a differential stain which allows us to differentiate bacteria based on their differences in their peptidoglycan and so remember we're going to look at this again but gram stain has the four steps and in the first step we use the crystal violet and the crystal violet and so let's go ahead and put the pen back on and so for gram-negative or i'm sorry for gram-positive bacteria gram-positive bacteria because they have the thick peptidoglycan they're going to retain the crystal violet and they're going to

stain purple so here these are our gram positive bacteria four gram negative bacteria because they have a thin peptidoglycan when we go to decolorize the decolorizer is going to shrink that very small layer of peptidoglycan and the dye this the crystal violet is going to come out of the gram-negative cells and so we're going to say gram-negative cells lose crystal violet and they stain pink because of safranin and safranin is going to be our counter stain and so we're going to walk through again the steps in the gram stain so when we look at the

four steps of the gram stain procedure remember that the first step is going to be the crystal violet step and the crystal violet is our primary stain and crystal violet is going to be a basic stain which remember means that the stain is positively charged and it's attracted to the negatively charged cell and so remember that when we look at gram positives and gram negatives the positive and negatives have nothing to do with the charge of the bacteria in both cases these bacteria are negatively charged the only difference between gram positives and gram negatives is

again the thickness of the peptidoglycan and so gram positives and gram negatives are both negatively charged cells and so we use a basic stain which has a positive charge and that basic stain that crystal violet is going to be used to stain both gram positives and gram negatives and so notice at this point in the staining procedure both are going to be purple then we add the iodine and the iodine remember is our mordant and what this does is it creates a crystal violet iodine complex and what that does is it makes those crystal violet

molecules larger to basically help to keep the crystal violet into the cells at this point both gram positives and gram negatives are both purple then we add our decolorizer and our decolorizer is going to be our alcohol acetone and remember that this is the most important step in the entire procedure and that's because this is where we get our differential stain if we time this just right what happens is is as we run the decolorizer over the cells or over the slide gram positives have that thick peptidoglycan gram negatives have the outer membrane and a

thin peptidoglycan and so as we add the decolorizer because this membrane is lipids it's going to dissolve and because it has a thin peptidoglycan that peptidoglycan is going to shrink and because it's so much thinner the dye molecules are going to go out of the gram negative and leave the cell if we do this properly gram-positive cells are going to retain the crystal violet and that's because they have a much thicker layer of peptidoglycan so again you have to time that just right in order for gram-negative to be clear and gram positives to be purple

then after we do the decolorizer step then we're going to use our safranin and safranin is our secondary stain or our counter stain and remember that that step is important because that allows us to stain the now colorless gram-negative bacteria in terms of gram positives remember that when we add safranin safranin is also a basic stain meaning that it is attracted to the negatively charged cell so for gram positives the saffronin still gets in but the purple dye which is the crystal violet is darker and those cells appear purple when we look at the gram-negative

bacteria which lost the crystal violet because of their thinner peptidoglycan when we now add the safranin or counter stain now the red dye stains the colorless cells and it allows us to be able to see the gram-negative cells and so notice that when the staining procedure is done gram-positive cells are going to be purple gram-negative cells are going to be reddish-pink and so this again is a differential stain it allows us to differentiate between closely related bacteria so we just finished looking at gram staining and remember that we said that for gram gram-positive or gram-negative

bacteria that most bacteria fall into one of those two categories about 95 percent of bacteria are considered to be either gram positive or to be gram negative now there are some bacteria that we call gram variable and what that means is that depending on when you look at the gram stain for that particular culture sometimes it might appear being gram positive other times it might appear being gram-negative an example of this would be for bacillus and clostridium and so think about when you think about bacillus and clostridium what structure do those two bacteria both produce

which they have in common and the answer is that they both produce endospores now typically when we think of bacillus and clostridium we would call those gram-positive organisms however if the cultures age meaning if they've been growing in culture for long periods of times they can start showing increasing numbers of gram-negative cells meaning that for that organism depending on when you gram-stain it sometimes it might appear gram-positive other times it might appear gram-negative and so now we're going to look at atypical cell walls so other types of cell walls that fall out of this gram-positive

or gram-negative and so the first one that we'll look at is mycobacterium tuberculosis remember that this is going to be an example of an acid fast bacterium and what that means is that their composition for their cell wall is atypical and what that means is that in the case of mycobacterium their cell wall is made of 60 mycolic acid so they still have a thin layer of peptidoglycan but outside of that peptidoglycan they have that mycolic acid and the mycolic acid is held together by a polysaccharide so meaning multiple sugars put together and so when

we look at mycolic acid remember that that type of cell wall is very waxy and very sticky and so one of the advantages to the bacteria for having mycolic acid is that the bacteria is very resistant to chemicals so it's more difficult to treat with antibiotics it's harder to clean using disinfectants they're much more resistant to chemicals in addition they are also resistant to dehydration remember that i said that if you look at bacteria most bacteria on a surface can only survive two to three days when we look at mycobacteria they're longer lived they can

survive on surfaces for up to six months and so that bacteria is very resistant to dehydration in addition it's also resistant to phagocytic digestion meaning that in your lungs your lungs have these types of white blood cells that are called alveoli macrophages and macrophages are cells that can do phagocytosis meaning they can send out those extensions take in the bacteria and normally those macrophages would then destroy that bacteria but because mycobacterium has mycolic acid in their cell wall what ends up happening is the macrophages can't digest the bacteria they were able to take them in

but they can't break it down and so what you get is these tubercules or these scar tissues that form in the lungs and the patients can actually start coughing up blood as a result only about two percent of patients get full-blown tuberculosis hiv patients are more likely to die from this this is one of the biggest killers in the world for hiv deaths meaning that oftentimes hiv can lead to a compromised immune system and then patients can actually die of a secondary infection because their immune system couldn't fight off for example this mycobacterium tuberculosis and

so this these bacteria are resistant to phagocytic digestion and again they're also going to be resistant to chemicals the next one that we're going to look at is going to be mycoplasma pneumoniae and this causes primary atypical sorry atypical walking pneumonia and so if you've ever heard this term walking pneumonia this is basically where you get an infection in your lungs but it's a less severe type of pneumonia meaning walking you might be able to still function and carry on yet have this infection in your lungs and so most um most pneumonia is actually caused

by streptococcus pneumoniae but a lot of lung infections are typically viral and when you get a viral lung infection sometimes you can then get a secondary infection from bacteria and so when a patient has this mycoplasma pneumoniae in their lungs and let's say the doctor decided to gram stain to try and determine what type of bacteria might be in the lungs it's often missed by a gram stain and the reason for that is that what makes mycoplasma unique is that they lack so they lack a cell wall they are one of the smallest bacterial cells

so they're about 0.2 micrometers which if you remember like e coli for example is about one micrometer these are one-fifth of that so they're even smaller than um most normal bacteria and in fact one of the reasons that it took so long for scientists to discover them is because they're so small originally when they were discovered they were mistaken for being a virus but they're not they're actually a bacteria because they lack a cell wall they are pleomorphic meaning they can take on multiple shapes and one of the problems with not having a cell wall

is that this bacteria is sensitive to dehydration and hypotonic environments and so what i mean by hypotonic environments we're going to talk more about this in a minute but hypotonic means that the solution outside the cell has a lower solute concentration remember solutes are things that can be dissolved and so if you have a lot of water outside the cell relative to inside what ends up happening is water will go into the cell now bacterial cells plant cells that have a cell wall the cell wall can help restrain how much water can get into the

bacteria in the case of mycoplasma because they lack a cell wall they are more sensitive to damage from water rushing in than other types of bacteria what ends up happening is that if too much water goes in the cells undergo lysis meaning that they break open and so to help to try and combat this defect by not having a cell wall they actually have these sterols in the cell membrane and the steriles are typically steriles are cholesterol-like meaning they're lipids and you're going to see in a minute that one of the functions of cholesterol in

the cell membrane is to help to maintain the correct fluidity and so because these bacteria lack a cell wall those sterols which are typically only found in eukaryotic cells these sterols are present in these cells to help to protect from this lysis to protect from the bacteria rupturing and breaking up now one of the problems with treating mycoplasma is that they can be difficult to treat with antibiotics because they lack a cell wall and so if you think about penicillin for example penicillin is an antibiotic you're going to see that targets peptidoglycan synthesis or cell

wall synthesis if peptide if if mycoplasma lacks a cell wall they don't have peptidoglycan meaning that penicillin would not be effective against them and so these are more difficult to treat because we don't have as many antibiotics that could be used to target this type of bacteria and so the last little part for this part is going to be to look at what are some of the things that can damage cell walls and so the first is going to be an enzyme called lysozyme and lysozyme is an enzyme normally found in perspiration or sweat um

in tears mucous and saliva and your body produces the lysozyme as a defense mechanism it's there to help inhibit microbial growth and what it does is that it actually breaks down or digests the disaccharides in the peptidoglycan and so because they break down that peptidoglycan that causes damage to the cells and when the cells get damaged they might die um as a result another example of a chemical that damages cell walls is going to be penicillin penicillin again is an antibiotic and the way that it works is that it inhibits those peptide bridges in the

peptidoglycan and so again notice that both of these inhibit peptidoglycan so what type of bacteria do you think might be affected most by lysozyme and penicillin is it going to be the gram positives or the gram negatives and so think for a minute and so you would come to the conclusion that these usually affect gram positive more and that's because gram positives have a thick layer of peptidoglycan and so because they have a thick layer of peptidoglycan um they are more sensitive to these chemicals however most of the organisms in your mouth are typically gram

positive for example if you happen to carry streptococcus piogenes that's the one that carries that causes strep throat streptococcus pyogenes is a gram-positive bacteria yet they have acquired adaptations that actually allow them to survive even in the presence of lysozyme and so they found a way basically to resist lysozyme but again typically lysozyme is going to inhibit peptidoglycan which means that typically both of these chemicals are more going to affect gram positives relative to gram negatives so i have a question for you and the question says the outer membrane of gram-negative bacteria contains red steriles

yellow mycolic acid green tachoic acid or blue lipopolysaccharide so i want you to pause think about your answer and then when you're ready go ahead and turn the video back on okay so if you said blue you're correct right so gram-negative bacteria in the outer membrane have the lipopolysaccharide so let's think about what bacteria have these other ones so when we look at steriles sterols again are found in mycoplasma and that's because mycoplasma lacks a cell wall and so to balance that they have the sterols or these cholesterols in their cell membrane mycolic acid which

bacteria have mycolic acid that's going to be our mycobacterium bacteria for artichoke acids artichoic acids remember are going to be found in gram positive only so gram negatives lacticoic acid gram positives have them and so again in the outer membrane this is going to be the lpf the lipopolysaccharides so now we're going to move on and talk about the cell membrane and so now we're going to move from cell wall in and so if we look at bacteria for example right this is going to be an example of gram-negative bacteria notice they have the outer

membrane they have peptidoglycan and then now we come inside to the cell membrane and so when we look at the cell membrane the cell membrane is what we call the fluid mosaic model and what that means is when we call the cell membrane a fluid mosaic that means that the membrane is a fluid structure meaning that it's not really rigid it's more kind of liquidy and fluid and the mosaic part of this is that for the cell membrane it has these mosaic are these different types of proteins embedded in the membrane and those proteins do

a variety of things that you're going to see in a minute if we look at a typical erythrocyte or red blood cell the erythrocyte has about 50 50 different types of proteins embedded in the membrane and that's only one cell type and so cells can have lots and lots of different proteins embedded in the membrane in addition one of the main components of the cell membrane remember is our phospholipid bilayer and our phospholipid bilayer remember is amphipathic it has a hydrophilic head so here's our hydrophilic head and it has this hydrophobic tail hydrophobic remains water

fairing so notice that the tail is primarily hydrocarbons hydrocarbons are nonpolar which means they don't have any charge to interact with water and so if you see this is how typically you'll see phospholipids simplified so here's the head and the two tails and so what happens is is these phospholipids self-orient themselves so that the heads face outside the cell and the heads face inside the cell where water is available and the tails orient themselves in the middle and that's to shield them away from the water and so you get this phospholipid biolayer these two layers

of phospholipids head space outside and inside the cell and the tails are shielded in the middle now what is the function of the cell membrane well if you think about prokaryotic and eukaryotic cells remember that we said that prokaryotic cells typically lack membrane-bound organelles meaning that they lack mitochondria mitochondria is a membrane-bound organelle that allows eukaryotic cells to carry out cellular respiration break down glucose convert it into atp chemical energy prokaryotic cells like bacteria don't have that membrane-bound organelle and you're going to see that part of cellular respiration takes place embedded in the membrane of

the mitochondria because bacteria lack that mitochondria it doesn't mean that they can't do cellular respiration they can they're still able to take chemical energy and convert it into atp but to do so they actually synthesize atp in their cell membrane and that's unique eukaryotic cells do not eukaryotic cells make atp in mitochondria prokaryotic cells make their atp embedded in the membrane of the bacterial cell and so that is one of the things that has to happen in bacteria in addition we also get nutrient processing meaning the membrane is going to be selectively permeable it's going

to regulate what goes into and out of the cell meaning we don't want anything and everything to come in and out but we also don't want nothing to come in and out and so the membrane is going to be used to transport things like glucose for example into and out of the cell and it also allows the bacteria to process those nutrients to basically um a lot of times there's enzymes that help break down those nutrients and so when we look at prokaryotic cells prokaryotic cells typically are going to lack steriles or they lack the

cholesterol in the membrane that eukaryotic cells will have and you'll see why that's important in a little bit so this is just showing you the fluid mosaic model and again what that means is that the membrane is a fluid structure and the membrane is about as viscous as olive oil so again you don't want it to be too solid another example of a lipid that's solid would be butter right you wouldn't want your membrane to be like butter so that nothing could get in and out you also don't want the membrane to be so fluid

that it can't regulate what goes into and out and so when we look at this phospholipid bilayer there's no covalent bonds holding those phospholipids together what's holding these phospholipids together are actually the hydrophobic interactions between the tails and that interaction is what's going to keep the membrane to be fluid because again if there were covalent bonds holding those together that's a rather rigid bond but because it's just hydrophobic interactions those are weak interactions and the phospholipids actually move side to side very freely occasionally they can rotate from one phospholipid leaflet to the other but that's

a lot less likely they can though go side to side and that's because they are this fluid structure and then there are proteins which you're going to see in a minute do a variety of things inside the bacteria so when we look at the cell membrane and we compare between prokaryotic and eukaryotic membranes there are several things that they have in common and the first is that primarily they're both made of a phospholipid bilayer and so we talked about the phospholipids when we looked at our lecture on macromolecules and in this case for the membrane

it's going to be primarily the phospholipid bilayer in addition there are the integral and the peripheral proteins which we just talked about that do a variety of different things inside the cell now in addition to similarities there are also differences between prokaryotic and eukaryotic cell membranes for example remember when we talked about cell walls and we talked about that there is a type of bacteria that lacks a cell wall and so think for a minute which of the bacteria that we talked about lacks a cell wall and the answer is going to be mycoplasma and

so for mycoplasma because they lack that cell wall they also have the sterols or the cholesterol embedded in the membrane to help keep the correct fluidity most eukaryotic organisms like animals use cholesterol as their steriles for fungi the sterile in the media or in the membrane is a little bit different it's something called ergosterol and so sterols are typically unique to eukaryotic cells except in the case of mycoplasma in addition for eukaryotic cells they often use carbohydrates embedded in the membrane that are used for both attachment and for cell cell recognition like we saw for

the glycocalyx so the cell membrane has four main components a phospholipid bilayer cholesterol proteins and something called glycocal and so we're going to talk about what do each of those four components do and if you recall back to our lecture on macromolecules we talked about phospholipids and remember that phospholipids are amphipathic meaning that they have both a hydrophilic portion and a hydrophobic portion and if you remember hydro is referring to water and if you think of a phobia a phobia is a fear right if i'm arachnophobic i'm afraid of spiders the hydrophilic heads are water

loving and for those those are going to face both inside the cell and outside the cell where water is present the middle part of the membrane are made up of these fatty acid tails and the fatty acid tails remember are hydrophobic they're water fearing and so they're actually shielded from the water that's both inside the cell and outside the cell and so the main component of the membrane is going to be this phospholipid bilayer and this is really important because the membrane is a very fluid structure and so the phospholipids themselves also help to maintain

the correct fluidity another component for the fluidity of the membrane is the cholesterol and when we think of cholesterol we typically have a negative connotation in our head right you think of oh i need to make sure my cholesterol is not too high but in fact your cells actually require cholesterol in order to function and so cholesterol in some instances is actually a good thing and the cholesterol in the membrane is there to basically keep the correct fluidity meaning that it prevents the membrane from packing in too tightly and making a very solid structure and

it also prevents the membrane from becoming too fluid in which it couldn't regulate what goes into or out of the cell and so cholesterol is very important in keeping the cell membrane the correct fluidity the next component are going to be the proteins and for the proteins we're going to talk about the functions in a minute proteins have a variety of functions in a cell if you think of an erythrocyte which is red blood cells erythrocytes have about 50 different types of proteins embedded in the membrane some of these proteins are what we call integral

proteins meaning that they're actually embedded in the membrane and some of these proteins are going to be peripheral proteins which are just associated with the membrane the next and last component is going to be the glycocalyx and these are basically going to be sugars that attach to proteins or phospholipids and they serve as binding sites and a cell lubrication and adhesion molecules they basically are there to help also with cell cell recognition meaning that two cells can recognize one another so we're going to talk for a minute about what do those proteins do in the

membrane and remember that i said that if we look at an erythrocyte which is a red blood cell a red blood cell has 50 different types of proteins and so you can probably imagine that if it has that many different types of proteins that they probably do very diverse things in the cell and so one of the things that proteins do in the membrane is for transport these are going to allow substances to flow through these hydrophilic channels some things can cross the membrane on their own to get into and out of the cell others

need a little bit of help and so that help is through these proteins and we're going to talk about these more later in the lecture another function is going to be for enzymatic activity and these basically are enzymes that are going to speed up chemical reactions they help chemical reactions to go faster and again at the end of this lecture we're going to spend a lot of time talking about what enzymes are and how they function another really important component of proteins in the membrane is that some of these proteins act as what are called

signal transduction pathways and basically what that means is that these receptors have what's called a ligand and a ligand is a signaling molecule and the ligand and the receptors are very very specific and when a ligand comes in and it signals and it binds to the receptor that initiates some sort of signal transduction pathway inside the cell that tells the cell what to do for example if you got a cut and you had a wound you probably know that that wound is not going to stay there forever eventually that wound is going to heal and

one of the things that's going to happen is the cells in the area of the wound are going to send growth factors to the cells in the area telling them to divide to repair the damaged tissue and so these growth factors get sent and the growth factors themselves are going to be the ligand and cells have receptors for those growth factors and that then sends a signal to tell that cell to divide and so these are called signal transduction pathways they're basically a way to relay a signal to allow cells to communicate with each other

another important function of a membrane is cell cell recognition and this basically is going to serve as identification tags recognized by other cells so if you remember in our cell lecture where we looked at the video of the white blood cell chasing the bacteria you'll remember that the white blood cell didn't engulf the red blood cells it recognized that those cells were self and that not to engulf its own red blood cells however it did recognize a signaling molecule on the bacteria and when it came to the bacteria you'll remember that it engulfed then it

took in that bacteria and so there are these proteins typically glycoproteins that help with cell cell recognition the next is going to be for intercellular joining so allowing two cells to join together and kind of holding them together and then lastly attachment to the cytoskeleton and what's called the extracellular matrix and this is basically there to help maintain cell shape and to coordinate changes to the cell shape and so this is going to be important for maintaining cell shape and so we're going to talk about now traffic across the membrane how do we get molecules

into or out of the cell and traffic across the membrane is essential you have to be able to get things into and out of the cell in order for the cell to survive and if you think about it for example think of your own cells if you don't eat your cells can't survive your cells need to be able to take in molecules for energy we're not plants we can't make our own energy and so the way that we get our energy is by eating food right and so our cells need to be able to take

in those sugars and take in those amino acids and take in all the others essential nutrients that our cell needs to survive and so obviously then cells need to be able to take in different molecules for energy they also need to be able to get rid of metabolic waste products so things that the cell no longer needs if you think of breathing for example right you breathe in oxygen and you exhale carbon dioxide and you're going to see later that the reason for this gas exchange is for cellular respiration and carbon dioxide is going to

be a waste product of cellular respiration and the cells need to be able to get rid of it and the cells will have the carbon dioxide leave it'll go through the bloodstream to the lungs and you exhale it out additionally cells need to be able to take in and expel many important ions sodium and potassium for example so if you look at this image here here are the sodium and potassium channels and neurons which are the nervous system cells that communicate with one another the way that neurons fire is simply through a change in the

distribution of ions and the way that these ions move is through these sodium or potassium channels and all an action potential or a neuron firing really is is a change in voltage which is a result of a change in the ion distribution across the cell membrane and so being able to move these ions is essential if we think about calcium right you probably have been told when you were younger that you needed to drink let's say milk for calcium for your bones so cells need to have calcium chloride chloride is an ion and chloride we'll

talk about later um a disease that results from defective chloride ions is or from defective chloride channels is going to be cystic fibrosis and cystic fibrosis causes these defective chloride channels and we'll talk about later about how that affects the movement of water across the membrane so when we look at the phospholipid bilayer remember that the bilayer is made up primarily of phospholipids and again phospholipids are amphipathic meaning they have these hydrophilic heads and these hydrophobic nonpolar tails and so the way that the membrane orients itself again is that the heads which are hydrophilic want

to interact with the water both outside the cell and inside the cell and the tails that are hydrophobic want to be shielded from the water and they're going to be in the middle so when we look at this membrane again there's a part that's hydrophilic and there's a portion that's hydrophobic and this is going to basically have an effect on what types of things can cross or do not cross the cell membrane so the things that can cross the membrane on their own are going to be things that are hydrophobic so hydrophobic and hydrophobic oil

and oil can interact with one another and so these hydrophobic molecules are going to be able to get through this hydrophobic core and get into the cell freely and so this is going to be things like steroids so think about testosterone estrogen which are steroid hormones those can cross the cell membrane on their own also small hydrocarbons remember that carbon and hydrogen similar electronegativities and so when they bond they're going to form non-polar covalent bonds meaning they're going to share the electrons equally and they're also going to be hydrophobic and so small hydrocarbons can cross

the membrane on their own as well as non-polar small molecules like carbon dioxide and oxygen because again if they're non-polar they're also going to be hydrophobic which will allow them to be able to get through this hydrophobic core of the cell membrane the things that cannot cross are things that are hydrophilic and that's because hydrophilic molecules cannot interact with this hydrophobic core so think of hydrophilic like water can't interact with oil which is like this hydrophobic part so a good rule of thumb is if something dissolves in water it can't cross the membrane on its

own and so that includes things like salt right if you remember back to salt salt is sodium chloride and those are ions and sodium is a positive ion chloride is a negative ion these are hydrophilic they'll interact with water and therefore they cannot get through this hydrophobic core and these ions can't cross the membrane on their own another example glucose right think of sugar for example if you took sugar and you dissolved it in your coffee it would dissolve and that's because sugars are polar and if they're polar they're hydrophilic and again things that are

hydrophilic cannot cross this hydrophobic interior of the membrane amino acids which are remember the building blocks for proteins those are also polar and therefore cannot cross this hydrophobic core so the things that cannot cross hydrophilic molecules charged ions or very large molecules all of those components make it so they cannot cross the membrane on their own and they need help so we're going to talk now about diffusion and diffusion is the movement of molecules or ions from a region of higher concentration to a region of lower concentration and so i want you to imagine for

a minute that you have a beaker of water or a glass of water if you take that glass of water and you put in drops of food coloring for example you'll notice that when you put that food coloring in those drops of dye don't stay as drops forever that dye is going to start to move and spread out it's going to go from its high concentration as a drop to the low concentration which is the water around it right because when you put the drop in the high concentration is where you put it in the

low concentration is going to be the water around it and so those dye molecules are going to move from a high concentration to a low concentration and they'll continue to move and they'll continue to spread out until eventually they're evenly distributed in the water and at that point we would say that they've reached equilibrium now when we talk about things going from a high concentration to low you'll hear the term going down the concentration gradient and if you think about it going from high concentration to low right so that dye going from its high concentration

to low that's a favorable reaction that will happen on its own i don't have to do anything to make those dye molecules spread out and so when we talk about a concentration gradient there's two ways things can go up a concentration gradient or they can go down and now think about which one is more favorable which one's going to happen spontaneously will things roll let's say down a hill or spontaneously will they go up a hill and you guys probably all know based on gravity that by default without anything happening things would go down a

hill that's a spontaneous process going down a hill doesn't require anything going up a hill though requires energy and so diffusion because we're going from higher lower and that's favorable and that happens spontaneously we say that that's moving these molecules down the concentration gradient and again this is a spontaneous process no energy is required but it is dependent on the thermal motion of molecules because remember that molecules have inherent movement they bounce around and if you think about what you learned back when you were a kid if you heat something up what happens to molecular

motion and if you think about it for a minute you might recall that if you heat something up molecules move faster and so if those molecules are starting to move faster do you think that diffusion is going to happen faster at warmer temperatures or at cooler temperatures and so think about that for a minute will it happen faster at warmer temperatures or at cooler temperatures and you might come up with that it's going to happen faster at warmer temperatures because at warmer temperatures molecular motion is going to speed up which means that those molecules are

going to move faster and they're going to evenly distribute at a faster rate and so again the molecules are going to bounce around and eventually spread out until they reach equilibrium and so here's a different example of this here on the left we have this beaker and it has a membrane and this membrane is permeable to the dye meaning that these molecules of dye can cross the membrane and so if we put dye only on one side these molecules of dye are going to move from their higher concentration on the left to the lower concentration

on the right but notice that the dye molecules don't exclusively go to the right some of them by chance will happen to go back to the left it's just that net movement meaning it's more going to be towards the right and those molecules are going to move towards the right until they evenly spread out at which point we would say that they're at equilibrium now when molecules reach equilibrium does that mean they stop moving and the answer is no molecules always move even at equilibrium it's just that those molecules don't have net movement meaning they're

not going one way or the other faster in either direction the movement to the right equals the movement to the left and so that's an important concept is molecules always move even at equilibrium so water also has thermal motion and it will also bounce around and work to spread out and water will also move down the concentration gradient meaning that it will go from its high concentration so that's what these brackets represent that refers to concentration so it's going to go from its high water concentration to its low water concentration and so to understand how

this works we need to kind of review and talk about water and so remember that water h2o is an oxygen covalently bound to two hydrogens and if you remember back to our water lecture you'll remember that water is polar meaning that even though oxygen and hydrogen share electrons they don't share equally and that has to do again with electronegativity and if you remember back to that lecture and we talked about electronegativity is oxygen or is hydrogen more electronegative and so remember that we said that the atom that is going to have a greater electronegativity is

going to be the one that has its outer shell more full and so if you remember back to oxygen oxygen has six valence electrons in its second shell of electrons which means that oxygen only needs two more to fill its outer shell hydrogen on the other hand has one electron in its first shell and it only needs one more to fill this outer shell so hydrogen is only half full whereas oxygen has six out of eight meaning it's more than half full and so if you think about oxygen and hydrogen that then means that oxygen

is more electronegative than hydrogen and what that means is that because it's more electronegative when they share electrons they don't share equally it's like a tug of war oxygen wants those electrons more and so the electrons are going to spend more time around the oxygen and less time around the hydrogen and so as oxygen pulls harder for those electrons oxygen gets a partial negative charge because electrons are negative and if the negatively charged electrons spend more time around oxygen it's a partial negative charge which means then that the hydrogens get a partial positive charge and

that's because the electron spends more time with oxygen which leaves hydrogens as just a proton and the electron is spending more of the time around oxygen so it's partially positive and so what you get is water again is polar it has a part that's partially negative which is the oxygen and a part that's partially positive which is the hydrogens now when we talked about solutes remember that a solute is something that dissolves in water so in this diagram this diagram is showing it as a sugar but it just as easily could be something like salt

right you know that you can dissolve salt and water so i'm going to show you a diagram using salt as an example because it's a little more simple and if you remember back to our lecture talking about salt salt remember is just simply sodium ions and chloride ions and sodium ions are positively charged chloride ions are negatively charged and so remember that when we talked about interactions between atoms opposites attract and so what's going to happen is that negatively charged chloride ion is going to be attracted to the partial positive hydrogens and we get these

hydration cells sodium on the other hand has a positive charge and it's going to interact with that partially negative oxygen and so what happens is the reason that salt dissolves in water is because the water molecules interact with the sodium and the chloride and they separate them from each other so if on the left you have a lower solute concentration and on the right you have a solid higher solute concentration that means that on the right side where we have more sugar we have less free water and what i mean by this is in this

case this membrane is selectively permeable and what that means is that some things can cross the membrane others cannot and in this case our solute is not able to get across the membrane only the water can move and so we can't say that the solute is going to move from the right to the left because it can't cross the membrane so what we need to focus on is which direction the water will move and so to think about which way the water will move wherever we have a higher solute concentration wherever that solute is present

water is going to be attached to it and if you remember the solute can't cross the membrane and so on this side where we have more more solutes we have less free water because the water is not free to move it's bound to the solute on this left side here we have a lower call lower concentration of solutes but we have more free water more water that's not bound to a solute that's free to move and so we have more free water here less free water here and remember that things are going to go always

from high concentration to low so it's going to go from its high concentration of water here to low concentration of water here and water is going to move to the right and it's going to start to fill up the tube on this side and so again just like all other molecules water is also going to move from a high concentration to low and when you're looking for which way water moves it's always going to be from the low solute concentration which is where you're going to have more free water to the high solute concentration where

you have less free water so either way is fine to remember if you want to remember that it moves from low solute to high solute but for me i would rather remember that things always go from high to low and so i always like to remember that it's going to move from here where it has more free water or a higher water concentration to this side where it has a lower water concentration and so this is going to be referred to as osmosis okay and osmosis is the diffusion of water now tonicity is the ability

of a solution to cause a cell to gain or to lose water and you always need to compare two solutions because water or a cell is only going to gain or lose water depending on solute concentration and in order for this to work it must be separated by a water permeable membrane meaning that water can move because how can a cell gain or lose water if water can't move and you have to be really careful when you start talking about tonicity because you need to pay attention to which of the two solutions you're referring to

and i'll talk about that in just a minute so the first one that we'll talk about is a hypertonic solution and if you think of a kid that's hyperactive do they have more energy or less energy and you'll probably recall that if a kid is hyperactive they have more energy so the word hyper refers to more the hypertonic solution is the one that has a higher solute concentration and so notice that in this case here in white this is our cell and our cell is placed in a solution and that solution has more solutes outside

and so we would say that the solution outside is hypertonic relative to the south because again hyper means more so this solution is hypertonic relative to the cell and remember that anywhere that solute is water is going to be associated with it so all these little red dots here are referring to water and notice that if there's more solutes outside that means that this outside solution has less free water notice that there's only in this case one water molecule that's free to move if we look inside the cell which has a lower solute concentration it's

going to have more free water because the solute concentration is lower and there's more water molecules that are free to move so inside the cell we have more free water and so think about it for a minute which way is the water going to move is it going to go into the cell or is it going to go out of the cell and so think about it so where is the water going to go and if you think about it it's going to go from its high concentration inside the cell to the low concentration outside

what you're going to see is that water is going to move out of the cell now we're going to talk about for each of these solutions what you're going to see in both an animal cell and in a plant cell and remember that a difference between plant and animal cells is that plant cells have a rigid cell wall animal cells do not and so this is going to affect the way that water moves in a plant cell versus an animal cell so in an animal cell when the water moves out from a hypertonic solution so

as the water goes out animal cells going to shrivel up for the plant cell the water's still going to go out but the whole cell is not going to shrivel up because it has that rigid cell wall instead you're going to see something called plasmolysis and what that means is that as the water goes out the cell membrane is going to shrink in away from the cell wall so it's like the membrane kind of collapses in but the cell wall stays out here and so in plant cells this is referred to as plasmolysis and you're

actually going to visualize this in lab this week now let's look at what's going to happen if you place a cell in a hypotonic solution and hypo is less so remember that if hyper is more hypo is the opposite it's less so in this case it's the solution with a lower solute concentration so in this case this the solution outside is hypotonic relative to the cell because it has a lower solute concentration compared to the cell and so when we look at water concentration remember that if we have more solutes inside less solutes outside that

means that we have more free water outside and so think about it which way is the water gonna move if you put a cell in a hypotonic solution and so if you think about it water is gonna go from its high concentration in the solution to the low concentration inside the cell and the water in this case is going to move into the cell and the way that i remember that is if you put a cell in a hypotonic solution water is going to go in the cell's going to swell and it's going to become

a big o so hypo cell's going to become a big o okay and so water is going to go in cell's going to swell and so that's going to look different if you talk about an animal cell versus a plant cell in an animal cell if you put it in a hypotonic solution the water is going to go in the cell is going to swell there's no cell wall to restrain how much water goes in and the cell's gonna lyse and it's gonna burst open think about for a minute if you've ever been dehydrated and

you had to go to the hospital to get an iv you probably know that if you go to the hospital they're not going to put pure water into your iv they're going to put a saline solution and that's because they don't want to create a hypotonic solution outside your cells so that all the water is going to rush in and your cells are going to burst or lyse open and you can actually die from water intoxication it's something called hyponatremia and it happens sometimes in marathon runners when they sweat too much if they drink just

pure water you create a hypotonic environment outside the cells too much water goes in and your cells would start to lyse and so again this is why in a hospital if you're dehydrated they're not going to put pure water in there they're going to put a saline solution that has some solutes so that you don't have too much water rushing into your cell if you think about a plant cell however if you water a plant you don't use salt water or saline to water your plant you just use tap water where the soil concentration is

low you are putting your plant in a hypotonic solution and in a plant cell that's actually a favorable reaction because as the water goes in it creates some pressure inside that cell and that makes the cell become target it creates what's called turgor pressure and that pressure inside the cell from the inside pushing on the cell wall that pressure is going to make the cell very rigid very firm and that's what allows the plant to stand upright it needs that tiger pressure so in a plant you want to put the plant cell in a hypotonic

solution because you want the water to go in to create that pressure but again animal cell not good to put it in a hypotonic solution because the water is going to go in no cell wall to restrain it and the water is going to cause the cell to go pop and burst open that's called lysis now back to the slide about tonicity and i said about always make sure to pay attention to which solution you're paying it or which solution you're talking about so notice in this case we can say that the solution the solution

is hypotonic but the cell we could also call hypertonic so we could say that the cell is hypertonic relative to the solution right it has more solutes relative to the solution so again always be careful when you're using the terms hypertonic and hypotonic which one are you referring to are you talking about the solution or are you talking about inside the cell and so in this scenario the solution is hypotonic relative to the cell or you could say the cell is hypertonic relative to the solution and the last scenario is if you put a cell

in an isotonic solution iso refers to same and this is where you have an equal solute concentration on both sides of the membrane so notice one two three one two three solid concentration is the same which means that the water concentration is also the same notice one two free water molecules one two and so what that means is you have an equal concentration of water on either side of the membrane and so think about that for a minute does that mean that the water won't move and if you think about it right you might recall

that molecules always move even at equilibrium and so it's not that you don't get any movement you just don't get net movement water is going to go into the cell and out of the cell at the same rate and so the water is equally going to move in both directions so if you put an animal cell in an isotonic solution water is going to go in and out at the same rate that's going to be a normal animal cell again you want your cells to be in an isotonic solution for a plant cell however that's

not a good thing again you want that pressure inside the cell in order to make the cell firm so that the plant stands up if you were to water your plant with an isotonic solution where the water is going into and out of the cell the cell's going to be flaccid and if it's flaccid it's not firm and your plant's going to wilt and so best scenario for an animal cell isotonic solution best scenario for a plant cell would be to actually put it in a hypotonic solution so that the water goes in and so

i have a class paper for you so if you're stranded on an island should you drink the ocean water to quench your thirst why or why not so when you're ready go ahead and pause this and think about your answer and write down what you would have answered had you been in class and then when you're ready go ahead and turn the video back on and listen to the answer so go ahead pause it okay so let's go over the answer so if you're stranded on the island should you drink the ocean water the answer

is no because if you drink the ocean water which is saltwater right think about what happens if you drink ocean water you're creating a hypertonic solution outside your cells which means there's more free water in your cells and the water is going to go out of the cells and that's going to cause your cells actually to become more dehydrated and so if this continued to happen this would lead to dehydration and in extreme cases death okay and so you would not want to drink pure ocean water because again drinking salt water would cause you to

become more dehydrated and then this last one here's a series of questions and the answers will be posted on blackboard for you to use to study so i want you to work on these and then after you've worked on these you can check your answers with those that are posted on blackboard and so this is going to conclude part one of the video and when you're ready you can go on to part two and we're going to start by talking about transport of molecules or ions across the membranes so how do things actually get into

or out of the cell so the first type of transport is referred to as passive transport and it's passive because no energy is required this is the used for the transport of molecules or ions down the concentration gradient and remember that that means moving things from a high concentration to low and going from high to low remember is down the gradient because that's favorable right if i put a ball on the edge of a hill it's spontaneously going to go down and same thing for molecules going from a high concentration to low that's a favorable

reaction right remember our beaker with water if i put dye into that beaker it's going to move from its high concentration as a drop to the low concentration in the solution surrounding it and so again passive transport is used to transport molecules or ions down the concentration gradient which is a favorable reaction and there are two main types of passive transport the first is going to be simple diffusion and in simple diffusion no transport protein is necessary this is used for things that can cross the plasma membrane on their own and remember that we said

that the things that can cross the membrane on their own without the help of a transporter are going to be things that are small hydrophobic and nonpolar and so things that are small hydrophobic and non-polar can get through that interior of the plasma membrane which is also hydrophobic so things like steroid hormones testosterone estrogen those are made of primarily hydrocarbons and hydrocarbons are nonpolar and therefore hydrophobic molecular oxygen so oxygen gas carbon dioxide those are both nonpolar they can cross the membrane all on their own the only thing the only requirement for passive or for

simple diffusion is that it's going to move from a high concentration to low and so notice that in the image that you see here it's going to move from its high concentration to low so the only thing that's required is a concentration gradient now in contrast to simple diffusion we have what's referred to as facilitated diffusion and this is basically that the diffusion is facilitated by these transport proteins so this is used for things that cannot cross the membrane on their own they still will go down the gradient meaning they'll go from the high concentration

to low but these molecules can't get through the hydrophobic core of the cell membrane and so what's needed is this transport protein and this transport protein like for example this one here that's a channel protein and it basically provides a hydrophilic corridor meaning that the amino acids from this protein that are in the middle are also hydrophilic which allow these hydrophilic molecules to be able to cross the membrane and so this is going to be used for ions and polar molecules an example of this aquaporins if you think of aqua you think of water porons

or pores aquaporins are channels that allow water to cross into or out of the cell there are also what are called carrier proteins and these are transmembrane proteins that not only provide a corridor for things to cross but they actually change their confirmation which is their shape upon binding to the solute so on one side it'll open up the solute will come in and bind the transport protein will change its shape and now open up to the inside and release that solute into the cell for example again these are going to go from high concentration

to low because they're passive transport they don't require energy this is in contrast to active transport and in active transport it requires both a transport protein to help move that molecular ion plus it requires energy and that energy that's required is usually in the form of atp and this type of transport is used to transport molecules or ions up the concentration gradient up remember if you were to push something up a hill up requires energy so you would have to put in energy to get a ball say up a hill same thing if you're going

to transport things up the gradient if you're transporting things up the gradient it requires energy and this is used to transport things from a low concentration to a high if you think about that beaker that's um that has water and has a drop of dye in it that dye remember is naturally going to go from its high concentration as a drop to the low concentration around it and if you think about it is that dye ever going to go from a low concentration to high meaning is it ever going to go from where it spread

out and all of a sudden spontaneously concentrate itself back into a drop and the answer is no things will not spontaneously go from a low concentration to a high concentration and so that requires energy which is why we call it active transport you actively have to do something to move these molecules or ions up the gradient some examples of this ion pumps for example here you're seeing a proton pump and a proton pump like you can imagine pumps protons protons are simply hydrogen ions remember that all hydrogen is a normal hydrogen atom is one proton

one electron when we talk about a hydrogen ion in a hydrogen ion it gives up its electron and what you're left with is h plus it has positive charge because all that's left is a proton so that's why we call h plus protons and in the proton pump we're going to pump hydrogens against the gradient so from a low concentration to a high and because that's an unfavorable reaction it requires energy in the form of atp now this type of pump is what we call electrogenic and what that means is that it generates a charge

difference across the membrane what we call a voltage so as we pump hydrogens into the extracellular fluid which is the fluid outside the cell you're creating an environment where the extracellular fluid is positively charged relative to the inside of the cell and so that's creating a voltage difference it's a difference of charge across the membrane another example that doesn't have a diagram here but is still important is the sodium potassium pump and sodium potassium pumps are used for neurons when a neuron normally does an action potential okay meaning that the neuron fires that is caused

by a change in the voltage across the membrane and in order to turn off that neuron again sodium and potassium pumps need to go against the gradient to reset that voltage so that the neuron can fire again and so again these are going to be electrogenic they generate a voltage or charge difference across the membrane cotransporters requires two trans membrane proteins one is going to pump a molecule up the concentration gradient so meaning it's going to go from a low concentration to high and one that's going to let the molecule flow back down the gradient

and so the downhill movement is coupled to the upheld movement of another molecule an example of this is a sucrose proton transporter and so if we look at this co-transporter here it's coupled with a proton pump and a proton pump is going to pump hydrogens against the gradient so again moving it from its low concentration to its high concentration out here now as hydrogens go down the gradient going from high to low that energy that it gives off by going down the gradient is enough to help sucrose get into the cell and so again this

is referred to as co-transport it is active though because it requires either atp or some other favorable reaction to power the movement against the gradient so now we're going to talk about bulk transport across the membrane so how do we get large bulky molecules either into the cell or out and we're going to talk about exocytosis and endocytosis exocytosis okay exo is referring to exit this is how the cell gets large things out of the cell and the way this works is that these lipid vesicles are made in the cell and eventually those vesicles fuse

with the plasma membrane and release the contents to outside the cell and if you remember in our lecture about cell structures we talked about the protein production pathway and in the protein production pathway proteins go from the rough endoplasmic reticulum they butt off in a vesicle that vesicle takes the protein it fuses with the golgi apparatus and the golgi apparatus is going to modify it's going to sort the proteins and it's going to ship them and that protein is going to leave in a vesicle and the vesicle moves along it fuses with the cell membrane

and it releases those secreted proteins out of the cell and so this is how a cell secretes materials like for example proteins again for a protein production pathway hormones so insulin for example insulin is made in pancreatic beta cells so in your pancreas you have a special group of cells that's responsible for producing insulin and when you eat your body recognizes that sugar is available so when you guys eat your blood sugar begins to rise and as your blood sugar goes up your body recognizes that there's sugar available and your pancreatic beta cells produce insulin

and they release insulin into the bloodstream insulin travels throughout your body and it serves as the signal to tell your cells to take up glucose because all the cells in your body require glucose for energy to make atp so for cellular respiration for example and so insulin is that signal that tells your cells that glucose is available and so cells in the pancreas need to release that insulin so that that hormone can go through your bloodstream and circulate and tell all the cells in your body to take up glucose this is also how neurotransmitters get

released and so the way that two neurons communicate with each other is that one neuron that's already fired is going to release a neurotransmitter to an adjacent neuron when that adjacent neuron receives that neurotransmitter now you get an action potential you get a a neuron to fire for the adjacent cell and so neurotransmitters are how neurons communicate with one another this is also how the cell membrane grows because if you think about it these vesicles that are made here are basically components of the cell membrane and so as these vesicles fuse with the cell membrane

you're going to increase the surface area of the cell membrane and you're going to increase the cell membrane now in contrast to exocytosis which is how we get things out of the south indo refers to in getting things into the cell and so endocytosis is how we get large molecules or particles into the cell one of these types one of the types of endocytosis is something referred to as phagocytosis and in phagocytosis you can think of this like cellular eating and what the cell does is it sends out these extensions and these extensions are referred

to as pseudopodia and if you remember back to our lecture on cell organelles remember that we talked about cytoskeletal elements and specifically we talked about actin and actin is the cytoskeletal element that's responsible for producing pseudopodia if you remember into our video of the white blood cell chasing the bacteria when that white blood cell came to the bacteria it sent out those projections and engulfed and took that bacteria into the cell that's phagocytosis okay and so the cell is going to send out these pseudopodia it's going to fuse the pseudopodia together and engulf that food

and other particles into the cell into a food vacuole and then that food vacuole can get broken down and take in the food or if it's not food if it's let's say bacteria okay the cell is going to engulf that bacteria the white blood cell will engulf the bacteria the bacteria remember would fuse with the lysosome and the lysosome would then break down that foreign bacteria and so this is used to ingest larger particles things like bacteria viruses fungi lots of food molecules for example all of these things would use phagocytosis this is in contrast

another type of endocytosis is referred to as pinocytosis pinocytosis is pinching in so the cell in this case does not send out extensions it simply pinches in and it creates kind of this pocket in this little pocket is going to take in any of the liquid that's outside here and it's a very non-specific type of endocytosis meaning whatever's out here is going to be incorporated into that vesicle and you can think of this kind of a cellular drinking because again it's not going out it's not taking in food all it's doing is the membrane is

pinching in any fluid that's outside is going to become incorporated into this vesicle and that's how the cell's going to get in some of the solutes that it uses and the last type of endocytosis is something called receptor mediated endocytosis so receptors are proteins and they have a binding site for a type of molecule referred to as a ligand and receptors are very very specific so if we look at this receptor it has a ligand that would bind to it and a cell would recognize when the ligand bound to the receptor and when it did

it would form this coated pit and it would take in large amounts of this ligand in a very specific manner because again these receptors are specific for certain ligands and so this allows the cells to take in very specific ligands very specific types of molecules example of this ldl so if you've ever had your cholesterol checked you've probably heard a little bit about ldl ldl stands for low density lipoproteins and these low density lipoproteins these are these cholesterol carriers and remember that cholesterol is important for the cell again even though we think of cholesterol as

being a bad thing cholesterol is needed um it's used to make steroid hormones like testosterone estrogen cholesterol is also used in the cell membrane in order to regulate the correct fluidity of the membrane and so one of the ways that cholesterol gets into the cells is that these ldls these cholesterol carriers ldls are going to carry the cholesterol and ldls bind to these ldl receptors these receptors that bind to ldl and when they bind it's going to take the ldl into the cell and out of the bloodstream and that's going to allow cholesterol to get

into the cell and so ldls compared to what we call hdls ldls take cholesterol towards the heart hdls so high density lipoproteins takes cholesterol away from the heart and so typically you want to have a lower amount of ldl because you don't want to take a bunch of cholesterol a bunch of lipids back to the heart and you want a higher number not too high but a relatively higher number for your hdls which are the ones that are going to take the cholesterol away from the heart and again this is referred to as receptor mediated

endocytosis it allows the cell to take in large amounts of a specific type of ligand so class paper for you familial hypercholestemia is a genetic disorder in which there are defective ldl receptors what is the likely outcome so think about it for a minute okay what would happen if somebody was born with defective ldl receptors what would be the result so i want you to think about it for a minute and then you're going to pause it while you're thinking and when you're ready go ahead and push play okay so if somebody is born with

defective ldl receptors what that means is that if their receptors don't work properly they're not going to be able to take in ldl and remember ldl are the cholesterol-carrying molecules and if they can't take in ldl what that means is that that ldl and therefore that cholesterol is still present in the bloodstream it's not going to come out of the bloodstream and what happens as a result is people who have this condition have genetically high cholesterol because their cells cannot take in the ldl to get it out of the bloodstream and so because it's not

taken up by the cell it's going to lead to an increase in ldl and cholesterol in the blood and if treated if left untreated heart disease can occur so if your parents have high cholesterol it's always a good idea to get checked because it could be a consequence of not necessarily diet but it could have to do with just simply genetics i'm one of those people i've had high cholesterol ever since i was a teenager no matter how much i exercised no matter how well i ate i always had high cholesterol and again that's because

i have defective ldl receptors so it's not that i'm getting too much cholesterol in my diet it's simply because my cells can't take in ldl and therefore the cholesterol stays in my blood and so if you happen to have high cholesterol you want to go and find that out and get on medication to lower your cholesterol now currently the medication that they prescribe for high cholesterol doesn't really fix the defective ldl receptors there's not really a good way at the moment to make functional ldl receptors instead what those drugs typically target if you take like

a statin which is like lipitor lovastatin there's a bunch of them basically those drugs don't target your ldl receptors instead they actually target the liver to stop making cholesterol because if you don't make as much cholesterol that will help to keep your cholesterol down and so just something to think about