Biology 1002B Lecture Notes - Lecture 12: Chromosome, Dna Ligase, Deoxyribonuclease
20 Apr 2016
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12. 4 mechanisms that correct replication errors. 12. 4a proofreading depends on the ability of dna polymerases to reverse and remove mismatched bases. If a newly added nucleotide is mismatched, The dna polymerase reverses using a built in deoxyribonuclease to remove the newly added incorrect nucleotide. Enzyme reverses using its 3" to 5" exonuclease to remove mispaired nucleotide from the strand. The enzyme resumes working forward now inserting the correct nucleotide. 12. 4b dna repair corrects errors that escape proofreading. Any base- pair mismatches that remain after proofreading are corrected by dna repair mechanisms. Mismatch repair mechanisms increase the accuracy of dna replication. Distortions provide recognition sites for the enzymes catalyzing mismatch repair. Repair enzymes move along the double helix, scanning the dna for distortions in the newly- synthesized nucleotide chain. Enzyme removes several too many bases, including the mismatched base, leaving a gap in the dna.
