Biochemistry 2280A Chapter 6: Topic 16 - DNA REPAIR
23 Aug 2016
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Describe and differentiate between the different kinds of commonly observed dna damage. Deamination is the spontaneous loss of an amino group from a cytosine to produce uracil. Dimer covalent linkage between two adjacent pyrimidine bases due to damage by ultraviolet radiation from sunlight. Dna replication can incorporate an incorrect nucleotide that it fails to correct via proofreading: explain the fundamental mechanisms of the major dna repair systems, excision of damaged strand segment. Involves nucleases which cleave the covalent bonds that join damaged nucleotides to rest of dna strand: repair dna polymerase fills in missing nucleotides. Binds to 3"-oh of cut strand and fills in correct nucleotides: dna ligase seals the nick, predict which repair mechanism will be used to repair a particular instance of dna damage. Mismatch repair removes replication errors that escape proofreading. Endonuclease nicks backbone of new strand, then exonuclease removes bases from nick to mismatch site, finally repair dna polymerase fills in the gap.
