DNA polymerase proofreading: 3′→5′ exonuclease
DNA polymerase corrects a mismatched nucleotide during replication using its:
Answer C: explanation for every choice
A
5′→3′ exonuclease activity, as in prokaryotic DNA polymerase I, removes RNA primers ahead of the enzyme.
B
5′→3′ polymerase activity adds nucleotides. It does not remove errors.
C
Correct. The polymerase backs up and removes the incorrect nucleotide from the 3′ end.
D
Endonucleases cut within a strand. Proofreading trims from the end.
TakeawayProofreading = 3′→5′ exonuclease: backing up to fix the last nucleotide.
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Reviewed 2026-11-05 by a medical student. Spot an error? Report it with question ID bb37.