Which statement describes a common step in DNA repair processes?

Which statement describes a common step in DNA repair processes?

• A. DNA ligase performs proofreading
• B. DNA polymerases proofreading each nucleotide against the template and remove incorrect nucleotides
• C. Helicase performs mismatch repair
• D. Primase completes the break in the backbone

Answer: (B)

DNA polymerase proofreading during replication is a common repair step. As nucleotides are added, the enzyme checks each new base against the template. If a mismatch slips in, its 3' to 5' exonuclease activity removes the incorrectly paired nucleotide, and synthesis resumes with the correct one. This intrinsic proofreading dramatically increases fidelity by catching and correcting errors right at the moment of incorporation, before the DNA backbone is fully formed. Other enzymes have different roles in DNA metabolism but don’t perform this direct, nucleotide-by-nucleotide correction: helicase mainly unwinds the double helix, primase lays down RNA primers, and ligase seals nicks after synthesis; mismatch repair operates on errors that escape proofreading, using separate pathways to correct mistakes after replication.

DNA polymerase proofreading during replication is a common repair step. As nucleotides are added, the enzyme checks each new base against the template. If a mismatch slips in, its 3' to 5' exonuclease activity removes the incorrectly paired nucleotide, and synthesis resumes with the correct one. This intrinsic proofreading dramatically increases fidelity by catching and correcting errors right at the moment of incorporation, before the DNA backbone is fully formed. Other enzymes have different roles in DNA metabolism but don’t perform this direct, nucleotide-by-nucleotide correction: helicase mainly unwinds the double helix, primase lays down RNA primers, and ligase seals nicks after synthesis; mismatch repair operates on errors that escape proofreading, using separate pathways to correct mistakes after replication.