Lecture6-reading.pdf - •*Read Chapter section 12.4 and 9.4 from the text.
 12.4 Mechanisms That Correct Replication Errors • • 12.4a

Lecture6-reading.pdf - •*Read Chapter section 12.4 and...

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*Read Chapter section 12.4 and 9.4 from the text. 12.4 - Mechanisms That Correct Replication Errors DNA polymerase rarely makes errors, most of the errors it does make are base-pair mismatches These errors can be corrected by a proofreading mechanism during replication or by a DNA repair mechanism that corrects mismatched base pairs after replication 12.4a - Proofreading Depends on the Ability of DNA Polymerases to Reverse and Remove Mismatched pairs Proofreading mechanism depends on polymerase ability to back up and removed the mismatched bases DNA polymerase will only continue replication if the previously added nucleotide is correctly paired Steps for proofreading by DNA polymerase (figure 12.19) Correct base pairing allows for stable hydrogen bonding A DNA nucleotide is mismatched DNA polymerase recognizes there is a mispaired base, it uses its deoxyribonuclease to remove the incorrect nucleotide Replication is resumed, but this time inserting the correct nucleotide 12.4b - DNA Repair Corrects Errors That Escape Proofreading (mismatch repair) DNA repair mechanisms correct any mismatched pairs that the polymerase proofreading missed When there is a mispaird base that’s not A-T or G-C they don’t fit together well and cause a distortion to the shape of
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  • Fall '13
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