LIFESCI 3 Chapter Notes - Chapter 12.3: Dna Mismatch Repair, Pyrimidine Dimer, Dna Glycosylase
Document Summary
Mismatch repair system (mmr): mismatched nucleotides incorporated by the replication. 12. 3 mechanisms of dna repair apparatus are corrected. Cell must discriminate between parental template and newly synthesized strand. Recognizes small loops of up to 4bp of unpaired nucleotides formed by template slippage or recombination. Dam methylase: enzyme that methylates dna at the n6 position of adenine within a 5"- Newly synthesized strand is unmethylated for a short period immediately after passage. Mmr proteins can identify and distinguish unmethylated new strand. Mismatches can then be repaired according to the methylated template. Mismatched base distortion in dna recognized by muts. Helicase ii unwinds dna in the direction of the mismatch. Unwinding and dna degradation stop when mismatch is excised. Single strand gap is left from mismatch to original incision at gatc site. Coated with ssb, filled by pol iii holoenzyme and sealed by ligase. Distance between the mismatch and gatc cleavage site can be more than 1000 bp.
