4.5.2007 - 4.5.2007 Mutagenesis and Repair Talking about...

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4.5.2007 Mutagenesis and Repair Talking about where mutations come from when you talk about mutagenesis o Already mentioned that something will cause a lesion, and then the lesion can lead to a mutation at replication o Nonetheless we are talking about where mutations come from Then we will talk about the repair part to talk about how each of the ways DNA can be messed up can be fixed First mutations we will consider are those that will arise spontaneously o Not created by any outside agents like a chemical acting upon DNA o They arise out of the chemical structure of the DNA itself o Bases on the interior connect to their respective sugars by a single covalent bond, sometimes that bond just breaks (bond between the base and the deoxyribose sugar’s one prime carbon) o What is still holding the deoxyribose sugar in place, the phosphodiester bond on either side (5’ carbon and its 3’ carbon) are each connected to a phosphate on the strand o Even though this bond is broken the deoxyribose will not go anywhere and the DNA backbone remains in tact o What holds the purine in place? Hydrogen bonds, 2-3 to the other base, but this will not hold for very long o So it is the base, not the deoxyribose that has vacated its position o What is still in DNA? Have an apurinic site or an APsite Because it doesn’t have its purine It could have happened on the other strand Single covalent bond between pyramidine and its deoxyribose might just break. Deoxyribose is still held up by 2 phosphates on either side but H bonds being the only thing holding the pyramiding in place will not hold it very long so it floats out of position and is gone leaving an apyrimidinic site (not having its pyrimidine) it is also abbreviated (AP site) Chemically an AP site is the same thing, the only way they differ is by what they used to be. What they are now is identical Is an AP site a mutation or a lesion? It doesn’t create any standard nucleotide (not looking at an A, T, G, or C in wrong one or wrong number) It creates something new, some new kind of damage. So it is a lesion o But if we are talking about it, it must somehow lead to a mutation…but most of the time it does not. If there is an AP site on the template strand, DNA polymerase (but we do not specify what kind of DNA pol because there is so much detail in this chapter that differentiating the minor things between prokaryotes and eukaryotes is needless) DNA polymerase goes along picking up dNTPs and connects it until it gets to the AP site, nothing base pairs with an AP site and so most of the time the DNA polymerase at replication will dissociate from the template at the AP site and move downstream and reassociate with the template where there is a primer and then start base pairing again new nucleotides together There was double stranded DNA before and then after once it reconnects but there is not a deletion because it doesn’t cut anything out Deletion, the sequence on either side have to be connected to each other by a
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This note was uploaded on 04/07/2008 for the course BIO 325 taught by Professor Saxena during the Spring '08 term at University of Texas.

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4.5.2007 - 4.5.2007 Mutagenesis and Repair Talking about...

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