BIO 2133 Chapter Notes - Chapter 15.5-15.6: Ames Test, Deoxyribose, Dna Glycosylase
1 Feb 2017
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15. 5 organisms use dna repair systems to counteract mutations. Essential to the maintenance of the genetic integrity of organisms and their survival. They counteract genetic damage that would otherwise result in genetic disease or cancer. Most common mutations are when an incorrect nucleotide is inserted by dna polymerase it has proofreading abilities polymerase reverses and acts as a 3" 5" exonuclease (replaces bad one) Base-base mismatches, small insertions, deletions that remain after proofreading is activated mismatch is detected, incorrect nucleotide is removed, mismatch repair correct nucleotide is inserted. Strand discrimination: synthesized strand based on dna methylation how does the system tell the template strand from the newly. Adenine methylase (lags behind polymerase) recognizes a dna sequence as a substrate, adds a methyl group to each adenine residue during replication. Before methylation, a repair enzyme recognizes the mismatch creates a nick in the backbone of unmethylated strand. Exonuclease: (before adenine methylase can come) of mismatch is reached.
