During prokaryotic DNA replication, DNA polymerase III occasionally incorporates an incorrect nucleotide. The enzyme corrects most of these errors immediately through its proofreading activity. Which enzymatic function of DNA polymerase III is responsible for this proofreading?
- A 5' to 3' polymerase activity
- B 5' to 3' exonuclease activity
- C 3' to 5' exonuclease activity ✓
- D Helicase activity
Correct answer: C. 3' to 5' exonuclease activity
Explanation
DNA polymerase III possesses a 3' to 5' exonuclease activity that removes misincorporated nucleotides from the growing strand's 3' end, allowing the polymerase to replace them with correct bases. This proofreading function reduces the error rate from roughly 10^-5 to 10^-7 per base pair. The 5' to 3' exonuclease activity belongs to DNA polymerase I and is used for primer removal, not proofreading.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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