BIO 209 Lecture Notes - Lecture 8: Pyrimidine Dimer, Ap Endonuclease, Dna Ligase
27 Oct 2016
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Document Summary
Photolyase binds to thymine dimers: uses visible light as energy to cleave the crosslink, base excision repair. In prokaryotes and eukaryotes: removes abnormal or chemically modified bases. Creates an ap site for recognition of enzyme ap. Glycosylases recognize specific base alterations: ap endonuclease removes backbone, dna polymerase adds new base, dna ligase reforms the phosphodiester bond, nucleotide excision repair. In prokaryotes and eukaryotes: removes large base defects. Thymine dimers, larger alkylated bases: unique mechanism. Exinuclease cuts in two places (on either side of the defect) to excise the large piec: repair of dna by nucleotide excision repair: In humans, many more proteins are involved: mismatch repair, detects newly synthesized strand. In bacteria, the newly synthesized strand is less methylated or unmethylated. Looks for methylated a in a gatc sequence. Excises and replaces with correct base: dna polymerase fills the gap, dna ligase reforms the phosphodiester bond.
