Which polymerase purely functions in replication?

Which polymerase purely functions in replication?

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

Answer: (D)

During DNA replication, the enzyme that does the bulk of new DNA synthesis is the replicative polymerase. In bacteria, that job falls to DNA polymerase III, which is highly processive and works on both the leading strand (continuously) and the lagging strand (in short Okazaki fragments) with proofreading capability. DNA polymerase I also has polymerase activity, but its main function is processing after synthesis—removing RNA primers and filling in the gaps it leaves—so it’s not the primary engine of replication. DNA ligase is not a polymerase at all; it seals nicks in the backbone after synthesis. RNA polymerase makes RNA, not DNA, and is used for transcription. Therefore, the enzyme that purely functions in replication is DNA polymerase III.

During DNA replication, the enzyme that does the bulk of new DNA synthesis is the replicative polymerase. In bacteria, that job falls to DNA polymerase III, which is highly processive and works on both the leading strand (continuously) and the lagging strand (in short Okazaki fragments) with proofreading capability. DNA polymerase I also has polymerase activity, but its main function is processing after synthesis—removing RNA primers and filling in the gaps it leaves—so it’s not the primary engine of replication. DNA ligase is not a polymerase at all; it seals nicks in the backbone after synthesis. RNA polymerase makes RNA, not DNA, and is used for transcription. Therefore, the enzyme that purely functions in replication is DNA polymerase III.