DNA Polymerase Proofreading
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DNA polymerase proofreads each newly added nucleotide, using an exonuclease activity to remove and replace a mismatched base before continuing synthesis.
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DNA polymerase pauses when a newly added base fails to pair correctly, then reverses to excise that base and try again.
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Proofreading corrects errors during synthesis itself — a distinct step from the repair mechanisms that act on DNA afterward.