GCSE Biology - DNA Part 1 - Genes and the Genome #63

in this video we're going to discuss dna chromosomes genes and genomes and by the end you should be able to describe what each of them are and understand how they relate to one another dna stands for deoxyribonucleic acid and it's the chemical that all of our genetic material is made of dna is a polymer which means it's made up of lots of similar units stuck together and there are actually two strands which are stuck together to form this so-called double helix which just means that it's a double-stranded spiral now if you to take all the

dna out of a single cell and you unraveled it into one long strand then that strand would be over two meters long so to stop this from getting all tangled up and so that it's compact enough to fit inside the nucleus it's actually separated into 46 different sections and each of these sections is actually a really tight coil which forms something we call a chromosome so we can say that each of our cells has 46 chromosomes in it however there's only really 23 different types because we have two of each type one from each of

our parents so we'd have two chromosome ones one from our father and one from our mother two chromosome twos and so on all the way to twenty three and we call each of these a pair the 23rd pair is a bit different though as these are the sex chromosomes of which there is an x chromosome and a y chromosome women have two x chromosomes which makes them female while men have one x and one y and that makes them male the really confusing thing about chromosomes though is that you'll often see them drawn like this

as though they're all in x shape however they only look like this just before cell division for example before they undergo meiosis or mitosis usually when our cells are at rest the chromosomes look more like this now a gene is a small section of dna that codes for a particular type of protein so you can kind of think of it as being a small segment of a chromosome this section of dna is basically a code for a particular sequence of amino acids and when these amino acids are combined in this particular sequence they form a

protein there are only 20 different types of amino acids but because they can be combined in so many different combinations they can actually make thousands of different proteins so as you can see dna determines which proteins the cell produces which in turn is going to determine what type of cell it will be for example a red blood cell would need loads of the protein hemoglobin because that's what transports oxygen around the body while muscle cells will need lots of the proteins that we use for muscular contraction lastly we have the genome which is just a

fancy term to describe the entire set of genetic material in an organism for example my genome would probably be quite different to strangers but it would be more similar to my parents genomes and if i had an identical twin then we'd have the same genome scientists have now worked out the complete human genome which is to say that they know the entire code that our dna holds as well as being generally pretty interesting this allows us to identify genes that are linked to certain types of diseases sometimes the genes may cause a particular disease in

which case we call it an inherited disease because you inherit the genes and therefore the disease from your parents in other cases the genes might just increase the risk of a certain disease for example the prca genes increase your risk of breast cancer either way though by looking at our genes doctors are often able to choose more effective treatments for us and scientists can use this information to develop better treatments another thing that we can do with genomes is trace the migrations of our ancestors for example we can see that all humans share most of

their genome but the small differences between different populations can tell us when they separated such as when humans left africa or when humans first traveled to north america and that's it for our part one on dna in the next video we're going to take a look at alleles genotypes phenotypes and the difference between homozygous and heterozygous so hopefully you'll give that a watch and i'll see you next time you