Difficulty: Easy
Correct Answer: Helicase
Explanation:
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:
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:
1) Identify the mechanical task: disrupt base pairing to create single-stranded templates.2) Helicase uses ATP to translocate and unwind duplex DNA.3) Other enzymes act on the unwound templates (primase/polymerase) or on backbone integrity (ligase) or topology (topoisomerase).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:
a) Polymerase synthesizes DNA but cannot unwind duplex DNA efficiently.c) Ligase seals nicks between fragments; no unwinding.d) Primase makes RNA primers; no unwinding.e) Topoisomerase manages supercoils; it does not continuously separate strands at the fork.Common Pitfalls:Confusing topological stress relief (topoisomerase) with actual strand separation (helicase).
Final Answer:Helicase.
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