What is the principal enzyme in DNA replication?

• A. DNA Polymerase
• B. RNA Polymerase
• C. Helicase
• D. Ligase

Answer: (A)

DNA polymerase is the enzyme that actually builds the new DNA strand during replication. It moves along the template strand in the 5′ to 3′ direction, adding complementary nucleotides to the growing chain and forming the backbone’s phosphodiester bonds. This action creates a new, accurate copy of the DNA, with proofreading capabilities to correct mistakes as replication proceeds. Other enzymes at the replication fork have different roles—unwinding the helix, laying down RNA primers to start synthesis, sealing gaps between fragments, and relieving supercoiling—but the polymerase is the one responsible for synthesizing the new DNA backbone. In bacteria the main replicative polymerase is DNA polymerase III; in eukaryotes, other polymerases handle the leading and lagging strands, but the central job remains building the DNA molecule.