Notes Feb 22 - Feb 22- F ig 25-26, pg 917, fig 25.30, fig...

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Feb 22- Fig 25-26, pg 917, fig 25.30, fig 25.27; etra figure, fig 25.32; 25.33 Fig 25.26 - DNA is subjected to damage all the time from the environment - Thymine dimers due to UV light o Thymines that are adjacent to each other dimerize forming a cyclobutyl ringbetwen adjacent thymine residues on the same DNA strand o Most common is thymine, but thymine-cytosine dimers form as well but not as frequently - Such pyrimidine dimers locally distort DNA’s base pair structure, interfering with transcription and replication - All living cells have repair systems for this kind of damge - There are 16 genes in humans whose genes are devoted to make proteins to fix this problem - Mutations in these genes are big problems- disease is exoderma pigaderma o Freckles, skin lesions, cancer, have to be totally protected from sunlight - Other kinds of chemical damage to DNA which require elaborate repair systems Fig 25.27 - Oxidatived amage o Guanine can be oxidized to 8-oxoguanine o When modified DNA strand is replicated, the oxoG can base-pair with either C or A causing a G-C T-A transversion o Guanine can also be methylated as the normal keto position which can mess up hydrogen bonding - Most common kind of DNA damage where BER happens o Cytosine going to uracil…which now pairs with adenine o Nitrites cause this oxidative deamination o 1 in 10^5 cytosines per generation of e.coli becomes a uracil, which has to be fixed by BER, or else the uracil in the next round of replication will bind with adenosine - BER uses specific DNA glycosylase that recognizes uracil, which is very nearly structured to thymine - Fig 25.30 - DNA glycosylase - Damaged bases that cannot be directly repaired may be removed and replaced in a process known as base excision repair (BER)
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- Specific glycosyslase for specific damage - Chops of the damaged based o Phosphodiester bond is still intact o Cuts the glycosidic bond leaving a deoxyribose residue with no attached base Apurinic or apyrimidinic sites (AP or abasic sites) also result from
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This note was uploaded on 09/14/2011 for the course BIO 362 taught by Professor Walikarzai during the Spring '10 term at SUNY Stony Brook.

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Notes Feb 22 - Feb 22- F ig 25-26, pg 917, fig 25.30, fig...

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