Which DNA replication enzyme has some proofreading function?

Which DNA replication enzyme has some proofreading function?

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

Answer: (A)

Proofreading during DNA replication relies on a 3' to 5' exonuclease activity that corrects mispaired nucleotides as soon as they’re added. The enzyme doing the bulk synthesis of new DNA strands in bacteria is DNA polymerase III, and it includes this proofreading function in its active site. That combination—burden of rapid synthesis plus immediate correction—keeps replication fidelity high, making polymerase III the enzyme most responsible for proofreading during replication. DNA polymerase I mainly handles primer removal and gap filling after primers are laid down, and transcription RNA polymerase isn’t involved in DNA replication at all, so it doesn’t contribute to proofreading the newly made DNA.

Proofreading during DNA replication relies on a 3' to 5' exonuclease activity that corrects mispaired nucleotides as soon as they’re added. The enzyme doing the bulk synthesis of new DNA strands in bacteria is DNA polymerase III, and it includes this proofreading function in its active site. That combination—burden of rapid synthesis plus immediate correction—keeps replication fidelity high, making polymerase III the enzyme most responsible for proofreading during replication. DNA polymerase I mainly handles primer removal and gap filling after primers are laid down, and transcription RNA polymerase isn’t involved in DNA replication at all, so it doesn’t contribute to proofreading the newly made DNA.