Biology 1001A Lecture Notes - Lecture 3: Dna Mismatch Repair, Dna Ligase, Deoxyribonuclease
6 Nov 2016
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Document Summary
Cycle 3 mechanism of proofreading: depend on dna polymerases ability to reverse and remove mismatched basepairs, only when the most recent paired nucleotides are correctly paired can dna polymerase continue to add nucleotides to the growing strand. If mispaired dna polymerase backs up and xes it with its built in deoxyribonuclease. Incorrectly paired bases are too large or too small to t together, this distorts the double helix. This distortion provides a recognition site for repair enzymes. The repair enzymes will search for a mispaired base: once a mismatch is found the enzyme will cut the dna backbone and remove a portion on both sides of the mismatch. The gap is lled by dna polymerase and sealed by dna ligase. The same repair mechanism (excision repair) also detects and corrects damage in dna caused by chemicals and radiation (like uv light) difference between insertion sequences, transposons and retrotransposons.
