Which enzyme catalyzes the 5'→3' elongation of a new DNA strand during replication?

Introduction / Context:
Multiple enzymes coordinate at the replication fork. Identifying which one directly adds deoxyribonucleotides to a growing DNA chain is foundational knowledge for molecular biology.

Given Data / Assumptions:

• Question targets the catalytic polymerization step.
• Standard fork proteins act with distinct roles: unwinding, priming, elongating, ligating, and topology control.

Concept / Approach:
DNA polymerases catalyze nucleotidyl transfer: the 3'-OH of the primer strand attacks the alpha-phosphate of an incoming dNTP, releasing pyrophosphate and forming a phosphodiester bond, extending DNA 5'→3'.

Step-by-Step Solution:

Verification / Alternative check:
In vitro, purified DNA polymerases synthesize DNA on primed templates; other fork proteins cannot catalyze chain elongation alone.

Why Other Options Are Wrong:

• Helicase unwinds duplex DNA.
• DNA ligase seals nicks after synthesis.
• Primase synthesizes short RNA primers.
• Topoisomerase I relaxes supercoils; no chain elongation.

Common Pitfalls:
Confusing primase (primer synthesis) with polymerase (DNA extension).

Final Answer:
DNA polymerase