thumb|250px|right| DNA polymerases adds nucleotides to the 3′ end of a strand of DNA. If a mismatch is accidentally incorporated, the polymerase is inhibited from further extension. Proofreading removes the mismatched nucleotide and extension continues.
thumb|250px|right| DNA polymerases adds nucleotides to the 3′ end of a strand of DNA If a mismatch is accidentally incorporated the polymerase is inhibited from further extension Proofreading removes the mismatched nucleotide and extension continues