okay so in this video we're going to talk about mutations now one of the things I've noticed about mutations is that when we say that word we tend to think about like negative consequences but in reality the majority of mutations are neutral and they are responsible for the huge diversity of genes found among organisms when we look at like human eye color for example blue eyes is due to a mutation that occurred 6,000 years ago so when we think about uh mutations we basically have two categories you have your small scale DNA mutations as well as your large scale chromosomal mutations uh what we're going to focus on in this video are these small scale uh point mutations that happen during DNA replication so let's take this double strand of DNA and let's see what happens if we were to go through S phase and have this strand replicate right so like here if we open up this isn't really how it happens right but if we um like unwind the double helix and we have a new strands being built like here we see it being built from 5 to three so here's maybe like the leading strand or something or the lagging whatever um but in the other strand let's say that d pimas three and makes a mistake and right here instead of adding an a it adds a c so it's an incorrect uh base pair so when we call these types of mutations uh point mutations it's because it happens at a single point now they're also known as substitution mutations because this like the a was substituted for a c so with this uh if we think about the whole point of DNA replication is to make identical daughter cells well like this would end up this uh chromosome would end up in cell number one and this would end up in cell number two made by mitosis so in actuality they wouldn't be identical daughter cells but only one of the cells would actually have the mutation but anyway so let's go ahead and see the significance of this so now let's pretend that uh these two genes let's say that the mutation happened in a gene um and now this Gene is going to be transcribed so here R polymerase does transcription on both of these template strands and you can see how originally um the RNA should have a u right here but instead the RNA has a g so this is kind of significant if you think about um when we read our messenger RNA in the process of translation when we divide the MRNA into codons um that point mutation changes the codon so originally it was like a a codon that coded for Serene amino acid and now that mutation um is coding for alanine so that primary structure that that primary sequence of amino acids in the polypeptide is now different and this can be significant depending on the chemical properties of the r groups and how it influences how that protein folds so when we look at point mutations there are a couple different kinds so um we're going to use this AGC as our original DNA and then our original codeon is ucg that codes for searing amino acid so in some types of point mutations um let's say that this third base u mutates in the DNA instead of a DNA polymerase 3 adding a cytosine it adds Adine or an a well that will change the code on but guess what because of the redundancy of the genetic code it still codes for Siri so over here we can see how you CG right here codes for searing but so does U seeu it's kind of cool when there's mutations in that third base you can kind of see like look at Proline there are four different codons that all code for Proline or Lucy so that's kind of nice that that third base sometimes it's not always disastrous to have a mutation sometimes it could have no impact and call that a silent mutation the amino acid didn't change however sometimes um we could have what's called a missense mutation and in a missense mutation uh the codon the new codon does code for a different amino acid and so this could have here let me move this right here this could have um a significance or have a significant impact on how the protein folds depending on the properties of the r groups so let's pretend the original amino acid was polar and in this missense mutation the new amino acid is also polar well it shouldn't have too much of an impact on how the protein folds up however if you have a polar replaced with a non-polar amino acid well now that will cause the protein to fold up differently and if you remember shape determines function so if we change the shape of the protein we potentially change the function and that could be bad could be good might end up as neutral it all depends on the situation okay and then we have a nonsense mutation now these are pretty can be pretty disastrous in a nonsense mutation it is still just just one nucleotide being switched out or being substituted in that one point but the resulting new codon is a stop codon now this is bad because then when you have the ribosome translating the MRNA when it gets to a stop Cod on it stops so you may end up with a like a protein that's not finished being built and you end up with like a nonfunctional protein so like here if you have like a mistake like this and then you have your um like a point mutation well now as you divide this up you have a stop coat on here so then as the ribosome builds the polypeptide it gets to a stop and now that polypeptide is not finished now it's possible if like a protein is a thousand amino acids long and the St stop codon is near the end well and it's like 995 amino acids well maybe it'll fold up just fine and maybe still work somewhat but if you have your stop C on happen early in the um in the like mRNA well then that could be pretty disastrous and that organism would be missing a protein okay so let's go ahead though and look at our other kind of um DNA mutation these ones are called frame shift I wanted to think about it is like we're Shifting the whole reading frame like how you divide the um mRNA into codons is shifted so basically in frame shift mutations you have either insertions where you add or you have deletions so let's look at our original strand of DNA and mRNA here okay so we can divide it into codons and then you get your polypeptide now in a deletion or an insertion oops this is where I want you to focus like down here in this area so what's going to happen in an insertion or a deletion is um some of the nucleotides are not added they're like deleted from the sequence so here oops let me move this for you let's move it up top so now this strand of DNA that we're going to use to make the RNA is a little bit shorter there were some nucleotides that were deleted so now our strand of RNA will also be different so now when we divide it by codons um well basically we had that like mutation happen somewhere in this area so initially like sorry that stop should have shown up later but I'm here like met was still the same everything leading up to where the deletion happened will be the same it's after the deletion our codons so you can see in the top here it should have been au but now what we have it it should be Au CGA a but basically this c um yeah the C uh was deleted and this U because right now you can see like we are this G and C from this next codon are now here so it's basically been shifted over because we deleted that U and C so now this is called a frame shift the reading frame like how we read it has all been shifted to the left and so now when we divide our codons they're going to code for different amino acids now what I showed here here was called a deletion mutation but you could very likely um have also an insertion where we add nucleotides and then likewise you would that would be like if you cut in line you know like you add some people to the line everyone shifts down uh the same logic your how you divide those codons um would be different like how you read them would code for different amino acids okay so those are frame shift mutations and those have a bigger impact than the point mutations because literally anywhere after the insertion or deletion is going to have a different sequence of amino acids and here you can see it actually ended up coding for a stock code on as we shifted so this like UGA which wasn't a stop code on up here is now a stop code on because remember we had two being deleted okay so let's go ahead and look here well what happens though if you have a frame shift or even a point mutation that happens in the intron region of a gene right so like if I have this DNA strand here and this DNA strand um I just colorcoded the introns to be like the red regions and then um the black represents the exons or the coding regions of this Gene so if we were to transcribe and make the messenger RNA you can see how the introns are going to be removed and now this black RNA right here represents all of the exons being expressed and then you would divide this into codons and um have a polypeptide however if you have like an insertion or a deletion or a point mutation happen um in an intron so let's say like right here I just had to be deleted so we had a deletion here and a lot of times students are like oh no well it's going to shift the whole reading frame and all of the um amino acids and the polypeptide will be different but will it let's think so right here now we have this intron so if I compare this intron to up here like that's where the deletion happened but really guys pause the video and step the exons the exons that are the part that are expressed and like kept are still the same so even though it was a whole like deletion in an intron it's going to be okay because oh and even check this out it just so happened that this this is a stop cat on so if you have a stop cat on even it's okay because it's going to be removed and as it's removed and the exons are spliced together now you can pause the video if you'd like and compare but these two mrnas are exactly the same so when we talk about mutations in order for a mutation to really have an impact on a phenotype or on the physical expression of traits or of genes it actually has to happen in a coding region of your DNA so in our DNA only one % of our DNA codes for genes and in those genes we have regions that are introns that are non-coding so like literally when we talk about mutations most of them are neutral uh every time your cells divide you get about 30 new mutations and errors however they're happening in noncoding regions so they're not having an impact on our phenotypes the mutation has to happen in an Exxon part that will be expressed to actually manifest or show up in that organism now I don't have a slide for this but the other thing I should point out is that for a mutation to be passed from parents to offspring um it actually has to happen in a sperm or in an egg so if I had a mutation happen in my skin cell that leads to skin cancer and then I get pregnant my baby won't have skin cancer because the mutation was not in my egg so um like mutations to inherit would have to occur um in the process basically of meiosis when making sperm or egg a mutation happens and then that mutation would end up in The Offspring okay so that is my discussion on small scale uh like point mutations substitution mutations and frame shift mut all right good job