Biochemistry 3380G Lecture Notes - Lecture 21: Proofreading, Homologous Recombination, Superoxide
8 Feb 2015
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Causes of dna damage: copying mistakes: dna polymerase makes an error about once every 107 nucleotides, possible outcomes: Mismatched base pair, causing a mutation in one daughter double helix. Insertion or deletion of one or more bases, potentially causing a shift in reading frame. Result of unrepaired replication error: becomes a permanent mutation because there is no way to tell there is an issue with an. Question: suppose cytosine in the sequence tcga is deaminated, and the base is only repaired after the dna undergoes one round of replication. Ttga: depurination: loss of entire guanine or adenine base, promoted by acid, result: blocks dna replication (can be overcome by error-prone translesion. It is able to synthesize part damage but it makes mistakes much more often than dna polymerase. Repair polymerase will use the 3" end as a primer and it will fill in the gap. The nicks eventually get sealed so this must happen within a certain time frame.
