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Current time:0:00Total duration:8:52

Impact of mutations on translation into amino acids

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Video transcript

so let's start looking at a short sequence of DNA and the letters I'm going to use these are the short hands for the various nucleotide bases that make up a sequence of DNA so let's say that I have some thymine thymine cytosine guanine cytosine thymine adenine thymine thymine and let's throw another thymine in there so that would be our sequence of DNA and what would be the corresponding sequence of RNA that it would be transcribed into if you remember this from previous videos pause this video and try to figure that out well the key thing to appreciate is if we're talking about base pairs and DNA adenine pairs with thymine cytosine pairs with guanine but if we're talking about pairing into RNA well then instead of thymine in the RNA you would have uracil so the RNA here is well the thymine in the DNA would correspond to an adenine in the RNA adenine guanine cytosine guanine adenine and now since this is an RNA stay instead of having a thymine right over here this would be a uracil adenine adenine adenine so this process that we just did this is transcription transcription transcription from DNA DNA to RNA now the next step if we're talking about the whole process of how does this information actually have an effect on the body is we're gonna go from the RNA and translate that into a protein and the way we do that we've seen this in previous videos is every 3 of these bases that's a codon and it codes for a particular amino acid now to figure out what amino acid it codes for we look at an amino acid translation table and there's different types that you might see this is the most typical type so the first base is a second bases a third base is G first base a second base a where in this cell third base is G and so that will code for the amino acid lysine so we could write ly s short for lysine here and we could have also gotten that from a different type of translation table for example you might see a circular one that looks like that but we would have gotten the same result AAG start at the center a a G codes for lysine then the next codon and if you're getting it as excited about this as I am I encourage you to pause this video and try to keep translating this the next codon is C GA c g a arginine arginine and then the next one is you a a you a a well here that this little black circular dot what does that mean well that means stop codon and sometimes they'll just write the words stop there so this is stop there is not an amino acid called stop this actually signals to and this is happening at a ribosome this is signaling for the translation process to stop this is the end of our of our amino acid chain of our polypeptide chain and so we will stop right over there but now let's do some interesting things let's think about situations where there are mutations where some of these bases may be something gets inserted maybe something gets deleted maybe something gets swapped out and so let's start with what's known as a point mutation so let's say this C gets swapped out for an a well if that happened then on the RNA strand all of a sudden this would be a uracil and if that is a uracil this a AG would still be there coating for lysine but this second codon is now different what would it now code for we'll see you a see you a it'll now code for leucine instead of arginine lue seen Leu this is fairly typical for a substitution mutation it might change a particular amino acid but sometimes it could be more significant for example if this G was swapped out for an A then this C on the DAR na would then be you and then what would happen well this first codon would still code for lysine but the second one would be you GA you GA now all of a sudden it codes for a stop codon and so the actual translation process would stop which could be a very very big deal if this DNA sequence if the thing if the normal non mutated polypeptide had to keep going on and on and on over here just happen to have a stop codon next but you could imagine if they had just you know another thousand codons before the end but all of a sudden you had a point mutation to stop early that would significantly affect the protein that is coding for now another type of mutation that typically has a fairly significant effect is a frameshift mutation and that's where something gets inserted and or deleted and shifts everything so for example instead of the a being swapped in for the G what if the a got inserted here so then our sequence would look like this T T C and then we have a and then you have G C T G C T a T TT so what just happened here this was our original sequence but the a got inserted here didn't replace the G and so everything got shifted to the right now what are we coding for well when we transcribe to RNA this will be a a G you see G a you a a a and now this first codon still codes for lysine we've seen that multiple times but what about this second codon the second codon over here you see G you see G that's serine we got a different amino acid and what's interesting is it's not just that one amino acid is changing we're gonna see that keeps happening so now we have a you a a you a here we have isoleucine so iso leucine right over here which is different than what we had before we now don't have a stop codon anymore and we would keep going on and on and so you could imagine a frameshift mutation where you either insert something or you take it out so that the whole frame gets shifted can have a dramatic impact on what it will transcribe and then translate for now lucky for us even though mutations are always going on there are many proofreading mechanisms in biological systems to make them less frequent than they otherwise would be and people are still understanding how these proofreading mechanisms fully happen another thing to appreciate is we often associate a mutation as being equal to a bad thing and often times it is a bad thing it what used to be a functional protein may not may no longer be a functional protein because the the amino acids the the coding got stopped short or there was a frameshift mutation it's just coding for completely different things so sometimes it could be very bad and some diseases actually are caused by strange mutations like that that show up oftentimes the mutation might not be a big deal maybe something it gets swapped out maybe only one amino acid changes and it doesn't really change the the ability of the protein to do its job in which case it doesn't matter but every now and then a mutation that could actually be a good thing in fact we need the mutation in order to have variation in a population and variation is what natural selection and evolution run off if you don't have variation then you're not going to have different things that get selected in different environments and you're not going to have that gradual change over time so a big picture hopefully you got a better appreciation for how transcription and then a translation let me write that down and then so that's transcription from DNA to RNA and then this is translation translation from RNA to to protein to protein we got appreciation of how that happens we got a pre shishun of how to use these translation tables but also how either a point mutation or a frameshift mutation can eventually affect the protein that gets coded for
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