AS.020.331 Lecture Notes - Lecture 22: Dna Repair, Dna Mismatch Repair, Dna Replication
Document Summary
Detection and repair of damage confined to a single strand of dna. Damaged region is recognized and removed my specific endonucleases. Usually, replication is blocked until dna damage is repaired (g1 checkpoint in cell cycle: if not, replication may proceed through an unrepaired lesion, which is not good. Cytosine can undergo spontaneous deamination: this creates uracil dna, uraci-dna glycosylase removes this uracil, gap repair fills in the empty space with a cytosine (abasic site repair pathway) Repair options: bypass repair, recmbination repair. Can fix damage occurring after replication but before mitosis (g2 checkpoint) Example: tobacco smoke causes a mutation: damaged base is removed by an excision endonuclease (exinuclease) This removes a small oligo that includes the base. The human oligo that is excised is approximately 29 base pairs. The e. coli oligo is 12 base pairs escape proofreading: the gap is filled by gap repair synthesis. Note: mismatched bases ~10^-(cid:883) bp, proofreading 3" 5" exonuclease ~(cid:883)(cid:882)^-8.
