Which enzyme is critical for the proofreading process during DNA synthesis?

The enzyme that is critical for the proofreading process during DNA synthesis is DNA polymerase. During DNA replication, DNA polymerase not only synthesizes new DNA strands by adding nucleotides complementary to the template strand, but it also has an intrinsic proofreading ability. This proofreading occurs through its 3' to 5' exonuclease activity, which allows the enzyme to remove incorrectly paired nucleotides immediately after they are added. This mechanism is essential for maintaining the fidelity of DNA replication and ensuring that errors in the DNA sequence are minimized, thus preserving genetic information.

In contrast, helicase is responsible for unwinding the DNA double helix, allowing access for the replication machinery, while primase synthesizes short RNA primers that are necessary for DNA polymerase to initiate synthesis. Topoisomerase alleviates the torsional strain created ahead of the replication fork by cutting and rejoining DNA strands, but it does not play a direct role in the proofreading of newly synthesized DNA. Therefore, the unique proofreading function of DNA polymerase is why it is deemed critical in this process.