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Unformatted text preview: After proofreading, the error rate is 1 in 1 billion (10 9 ) base pairs. Mismatch Repair After DNA is replicated, some enzymes function to locate mismatched base pairs, remove a short segment of nucleotides containing the error, and replace the segment with the correct nucleotides. The new segment is then sealed to the original strand by DNA ligase. Recall that this is the enzyme that seals the Okazaki fragments during DNA synthesis. When repair enzymes detect a pairing error, how do they know which DNA strand contains the error? The repair enzymes are capable of distinguishing between the original strand of DNA and the new strand that contains the error because the new strand is not methylated . Methylation involves adding methyl groups (CH 3 ) after DNA is synthesized. Shortly after DNA is synthesized, however, the new strand is not yet methylated. . Mismatch repair enzymes are able to detect which strand is not methylated....
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- Fall '10