DNA transactions — Which enzyme is responsible for unwinding (unraveling) short segments of duplex DNA ahead of the replication fork?

Introduction:
DNA replication requires coordinated activities to open the duplex, synthesize primers, extend strands, and relieve torsional stress. This question targets the specific enzyme that separates the two strands at the fork.

Given Data / Assumptions:

• Duplex DNA is stabilized by hydrogen bonds and base stacking.
• Replication forks move directionally along the template.
• Distinct enzymes perform unwinding, priming, polymerization, ligation, and supercoil relief.

Concept / Approach:
Match each replication enzyme to its primary function: helicase unwinds; primase synthesizes RNA primers; polymerase extends DNA; ligase seals nicks; topoisomerase relieves supercoils but does not drive strand separation at the fork.

Step-by-Step Solution:

Verification / Alternative check:
Loss-of-function helicase mutants stall forks despite intact polymerase activity, confirming helicase’s essential unwinding role.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing topological stress relief (topoisomerase) with actual strand separation (helicase).

Final Answer:
Helicase.