How are Proteins Made? - Transcription and Translation Explained #66

[Music] in today's video we're going to take a closer look at protein synthesis which is the process of making proteins we can think of this in terms of two steps transcription and translation in a nutshell transcription is the process of taking a single gene of dna and copying it into a structure called mrna then translation is the process of taking this mrna strand and using it to produce a protein before we go through the details though we need to look at why we actually need these two steps inside almost every cell is a nucleus that

contains all the genetic material of that cell in the form of dna the reason we say dna is so essential to life and controls what the cells do is because it contains thousands of genes which are each small sections of the dna that have a specific sequence of bases and so are able to code for a specific sequence of amino acids which when combined will form a particular protein in order to actually make a protein though the specific sequence of bases has to be read by one of these structures called ribosomes which importantly are outside

of the nucleus however because the dna is so big it can't leave the nucleus itself and so if we want to use a gene to make a protein we're gonna have to make a copy of that gene first and because we're only copying a single gene rather than the entire dna strand the copy will be small enough to leave the nucleus and so it can make its way to the ribosome now this copy we're talking about is mrna which stands for messenger rna and is just a copy of a single gene the structure of mrna

is mostly similar to dna but it does have a few important differences that you need to know about for one is much shorter than dna because it's only a single gene long it's also only a single strand rather than a double strand like dna and finally instead of containing the base thymine it contains uracil now that we've got these basics covered let's take a closer look at transcription and see how this mrna is actually formed in the first place in this image here we can see a small section of dna that contains two strands coiled

into a helix this is how it's normally found in the nucleus but to make it easier to understand transcription let's uncoil the two strands and show it using this simplified diagram instead to be clear though this is the same piece of dna as above we're just showing the two strands side by side rather than wrapped around each other and we're showing the bases as their letters so a for adenine t for thymine and so on for the sake of our example let's say that this region here between these two lines is the gene that we

want to copy even though in real life genes are normally much bigger than this the process starts with an enzyme called rna polymerase which binds to the dna just before where the gene starts then just ahead of the rna polymerase the two strands of dna separate apart so that all of their bases are exposed then the rna polymerase is basically going to move along the dna strand and read the bases one by one and use them to make an mrna strand for this to make sense though you need to remember that the mrna bases will

always be complementary to the dna bases so ac on dna will always pair with a g or an mrna g will pair with c t with a and then the odd one out is that if you have an a on the dna strand it's going to pair with a u on the mrna strand because mrna doesn't have t like we said a minutes ago all of the thymines which are the t's have been replaced with the uracils which are used in mrna so an a on dna will be complementary to a u on mrna so

in our example here the rna polymerase will start with this c base and so we'll start the mrna strand with a complementary g base next it will read the t base so it adds a complementary a to the mrna then it will move on to this a base and add a complementary u then go to the g and add the complementary c and then so on so the rna polymerase is going to carry on doing this building up the mrna base by base as it moves along the entire gene one thing to notice here is

that the dna strand keeps on separating just ahead of the rna polymerase and closing just behind it so that only a small section of the dna is ever exposed once it's moved along the entire gene and finished making the mrna strand the rna polymerase detaches from the dna and the dna strands can close back up this means we're left with an mrna that's then free to leave the nucleus and head off to the ribosome one last thing to mention though is that this strand of dna which the rna polymerase moved along is called the template

strand so it's the template strand which is used to make the mrna so going back to our whole cell for a minute we've now got an mrna copy of the gene here inside the nucleus which is free to leave the nucleus and make its way to the ribosome where it can undergo translation to produce a protein to help understand this part it's important to remember that for both dna and mrna each group of three bases which is called a triplet or codon codes for a specific amino acid to make proteins our cells use 20 different

amino acids and each one has a different three base codon for example this triplet agu codes for the amino acid serine whilst cca here codes for proline you don't have to remember these examples we're just using them to illustrate the point so let's now zoom in to a single ribosome and go through the process of translation to start the process off our mrna strand and the ribosome both bind together and we're now ready for the ribosome to start building the protein by adding one amino acid at a time the amino acids themselves are brought to

the ribosome by molecules called trna which stands for transfer rna trna molecules have the amino acid at the top and an anticodon at the bottom the anticodon is this sequence of three bases which are complementary to these three bases on the mrna and it's these three bases on the mrna that code for the amino acid that the trna is carrying so because each type of trna molecule is specific to a particular triplet on the mrna it can ensure that it always brings down the correct amino acid for example because the first triplet of our mrna

sequence here is a gu it will attract this trna molecule with the anticodon uca because uca is complementary to agu and the trna brings with it the amino acid serine because agu is the code for serine meanwhile this second triplet cca will attract this trna molecule with the complementary anticodon of ggu and that will be carrying the amino acid proline because cca codes for proline now the whole point of this seemingly complex process is that the trnas have now brought the correct amino acids down to the ribosome in the correct order so the ribosome is

able to join them together and start building up a chain of amino acids once it's joined these first two amino acids together the ribosome moves along the mrna slightly and so another trna molecule will come down and binds to its complementary codon on the mrna bringing with it the next amino acid this allows the first trna molecule to detach and repeat the process but importantly it leaves the amino acid behind this same process then repeats all the way along the chain until the ribosome reaches the very end and has joined together a complete chain of

amino acids at this point the amino acid chain will detach from the ribosome and then finally the chain can fold up on itself to form a protein anyways that is finally the end of this video so i really do hope you found it useful if you did then please do give us a like and subscribe and cheers for watching