so this video is going to be about mutations and protein structure so mutations are the ultimate source of new genes because they're going to change the sequence of nucleotides in our DNA so an example of a kind of mutation is point mutations so that's going to be a change in a single nucleotide pair within a gene and an example of a condition that can be caused by a point mutation is sickle-cell disease so we can see right here that sickle-cell disease results because of a change in a single nucleotide pair within this gene which is going to result in the substitution of glutamic acid with a valine and so when we have this valine it causes kind of a malfunction in the hemoglobin protein in our red blood cells which results in this condition which we call sickle-cell disease so some small-scale mutations so they can be caused by insertions and deletions so that would be the addition or the loss of nucleotide pairs that can oftentimes result in some pretty disastrous effects and so the way that it would do that is by causing a frameshift mutation so if we get a frameshift mutation then that means that the number of nucleotides that was inserted or removed from this gene was not a multiple of three because if we remember our codons are made up of three nucleotides so our DNA in our mRNA is really read by groups of three so if we take out a number of nucleotide pairs that's not multiple of three then it's going to throw off the organization of the remaining codons and result in a different protein than what would have been made originally and so another thing that can cause these mutations are mutagens so those are going to be physical and chemical agents that can interact with our DNA and cause mutations so now we'll look at some of the mutations that these can actually cause so first we'll have a silent mutation so in a silent mutation if this new nucleotide pair has no effect on the encoded protein so we encode the same amino acid as we would have originally even though we've changed one of the nucleotide pairs that's called a silent mutation because it doesn't do anything there's no visible effect on the phenotype of that individual or on the function of that protein so moving on if we change a nucleotide pairing and that results in the substitution of one amino acid with a different amino acid then that's called a missense mutation so in a missense mutation we have a change of the nucleotide sequence that results in one amino acid being switched out for another one and so that one depending on the characteristics of the old amino acid and the new amino acid could have you know really disastrous effects on the structure and function of this protein or it could not matter too much but that would depend on those two amino acids specifically so moving on we have nonsense mutations so when we have this nucleotide substitution again we change out one nucleotide for another in nonsense mutations that changes this codon into a stop codon instead of a codon for another amino acid and so this can be really disastrous because this stop codon is going to prematurely stop the translation of this protein so we end up with something called a truncated protein and so these truncated proteins are more often than not going to be unfunctional so they're not going to work at all and so a mutation that results in the formation of a new stop codon so this nonsense mutation can be really disastrous for a cell I hope you found this video really helpful all images unless otherwise stated are from Campbell biologies 11th edition remember that if you are an enrolled Baylor student we do offer free tutoring on the first floor of the SID Richardson building you can schedule a free one on one 30-minute appointment or you can drop in during any of our normal business hours for more details visit www.ajustlock.com