BIOLOGY 207 Lecture Notes - Lecture 23: Purine, Photolyase, Dna Replication
Document Summary
Oxidative deamination of bases, formation of apurinic sites. Losing purine residue: damage caused by reactive oxygen species. Dna repair is divided into two types: error-proof repair pathways , which prevent mutations. Methyl mismatch repair, photoreactivation, nucleotide excision repair, base excision repair, and recombinational repair. Error-prone repair pathways , which risk introducing mutations (the sos response) Operate only when damage is so severe that the cell has no other choice. A single-stranded segment of undamaged daughter strand is used to replace a gap in damaged daughter strand. Works on any damage that causes gaps during replication. steps. 1. replication fork approaches thymine dimer: dna polymerase skips damaged region, Leaving a gap where the damage is located: the reca protein binds to the sister double helices at the single-stranded segment. The sister copy being replicated that does not have this gap. These bases can be used as a template to fix this damaged and this gap.
