Name the enzyme that catalyzes template-directed synthesis of DNA during replication

Introduction / Context:
Multiple enzymes collaborate at the replication fork. The central catalytic activity that elongates DNA strands belongs to the DNA polymerases, which add deoxyribonucleotides to a primer in a template-directed manner.

Given Data / Assumptions:

• Reaction: polymerization of deoxynucleoside triphosphates into DNA.
• Directionality: 5′→3′ chain growth with a primer and template.
• Other fork proteins have different supporting roles.

Concept / Approach:
DNA polymerases catalyze phosphodiester bond formation, requiring a 3′-OH and a base-paired template. Helicase unwinds duplex DNA; gyrase relieves supercoils; ligase seals nicks between Okazaki fragments; primase lays RNA primers that polymerase extends.

Step-by-Step Solution:
Identify the reaction: DNA synthesis.Map enzyme to reaction: DNA polymerase performs chain elongation.Exclude accessory enzymes that enable but do not catalyze DNA polymerization.

Verification / Alternative check:
In E. coli, DNA polymerase III holoenzyme is the main replicase; DNA polymerase I removes RNA primers and fills gaps; eukaryotes use Pol α (primase), Pol δ/ε for elongation.

Why Other Options Are Wrong:

• Gyrase: topological management, not polymerization.
• Ligase: joins nicks, no base addition.
• Helicase: unwinds DNA, no polymerization.
• Primase: synthesizes short RNA primers, not DNA extension beyond its brief role in eukaryotic Pol α complex.

Common Pitfalls:
Attributing the core polymerization to “ligase” or “helicase” due to their high visibility at the fork.

Final Answer:
DNA polymerase