Mutagenesis and Repair (4-0-07)

Mutagenesis and Repair (4-0-07) - mutagenesis repair...

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4/5/07 mutation- heritable change in DNA in prokaryotes and eukaryotes, in cells there are a lot of ways other mutations can come about other than some agent changing one nucleotide into another nucleotide. Mutations have to be copyable, still made out of nucleotides, but that’s not necessarily how that happens. Lesion- some kind of DNA damage that does not create a standard nucleotide. Instead it creates a non-standard chemical structure in DNA. It is therefore not heritable because it is not something that DNA polymerase can reproduce or incorporate into the new strand. We still talk about lesions because lesions often cause mutations. In replication, DNA polymerase comes upon the lesion in the template strand, and because the lesion does not base pair the same way as the original nucleotide would have base paired, DNAP inserts an incorrect nucleotide or an incorrect number of nucleotides in the new strand. Lesions on one strand of DNA can often cause a mutation on the other strand of DNA at replication. Lesions will not have names like insertion, deletion, transversion, etc. Spontaneous- arise out of the structure of DNA and out of the replication of DNA itself. See diagram. The covalent bond between the sugar and the base on the 1’ carbon sometimes breaks, so now it is held together by the phosphodiester bonds on 3’ and 5’ carbon. Now that base disappears, and the deoxyribose appears without a base. Chemically, both “AP sites” are the same. The only difference is what used to be there. What’s the effect? Most of the time, this does not lead to mutation. If there as an AP site on the template strand during replication, DNAP cannot pick up anything that can base pair with an AP site! The DNAP will dissociate from the template right at the AP site. It will move down the strand, re-associate with the template when there’s a new primer, and then continue. What did it left behind? A single- stranded “gap” of DNA…it’s not a deletion, so what is it? This is the usual situation. DNAP comes upon AP site, instead of dissociating, it will stay in place. In a special situation, it picks up a random nucleotide onto the 3’ end of the new strand, creating a substitution- could be either transversion or transition. Or, what
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could also happen (still under special circumstances), DNAP gets to the AP site, doesn’t pair it with anything, but instead moves to the next nucleotide, base
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This note was uploaded on 04/27/2008 for the course BIO 325 taught by Professor Saxena during the Fall '08 term at University of Texas.

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Mutagenesis and Repair (4-0-07) - mutagenesis repair...

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