Which DNA replication enzyme functions in DNA repair?

Which DNA replication enzyme functions in DNA repair?

• A. DNA polymerase I
• B. DNA polymerase III
• C. DNA ligase
• D. RNA polymerase

Answer: (A)

In DNA repair, you need an enzyme that can both remove damaged nucleotides and then synthesize the correct DNA to fill the gap. DNA polymerase I in bacteria has this dual capability: it has a 5' to 3' exonuclease activity that removes damaged bases or RNA primers, and its 5' to 3' polymerase activity then fills in the missing stretch with new DNA. This makes it a repair-capable enzyme. DNA polymerase III, by contrast, is the main workhorse for rapid DNA synthesis during replication, focusing on elongation rather than repair and lacking the same exonuclease function needed to remove damaged segments. DNA ligase seals nicks after synthesis but doesn’t perform the DNA synthesis or repair removal itself. RNA polymerase synthesizes RNA, not DNA, and isn’t the repair enzyme used to replace damaged DNA with proper nucleotides. So the enzyme that functions in DNA repair is the one that can remove damaged DNA and replace it with correct DNA, which is DNA polymerase I.

In DNA repair, you need an enzyme that can both remove damaged nucleotides and then synthesize the correct DNA to fill the gap. DNA polymerase I in bacteria has this dual capability: it has a 5' to 3' exonuclease activity that removes damaged bases or RNA primers, and its 5' to 3' polymerase activity then fills in the missing stretch with new DNA. This makes it a repair-capable enzyme.

DNA polymerase III, by contrast, is the main workhorse for rapid DNA synthesis during replication, focusing on elongation rather than repair and lacking the same exonuclease function needed to remove damaged segments. DNA ligase seals nicks after synthesis but doesn’t perform the DNA synthesis or repair removal itself. RNA polymerase synthesizes RNA, not DNA, and isn’t the repair enzyme used to replace damaged DNA with proper nucleotides.

So the enzyme that functions in DNA repair is the one that can remove damaged DNA and replace it with correct DNA, which is DNA polymerase I.