During DNA replication, which enzyme primarily separates the two strands by breaking hydrogen bonds at the fork?

Introduction / Context:Unwinding parental DNA is essential to expose single-stranded templates for polymerases. The question targets the identity of the unwinding enzyme at replication forks.

Given Data / Assumptions:

• Replication involves coordinated action of helicase, primase, and polymerases.
• The task is to break hydrogen bonds between complementary bases.

Concept / Approach:Helicases are ATP-dependent motors that translocate along DNA and disrupt base pairing to create single-stranded regions.

Step-by-Step Solution:1) Helicase loads at the fork and uses ATP hydrolysis for movement.2) As it moves, it breaks hydrogen bonds and opens the duplex.3) Single-stranded binding proteins stabilize the exposed strands for replication.

Verification / Alternative check:In vitro systems without helicase show minimal fork progression; adding helicase restores unwinding and synthesis.

Why Other Options Are Wrong:DNA polymerase synthesizes DNA rather than unwinding; “strandase” is not a standard enzyme; “none” conflicts with well-established fork biochemistry.

Common Pitfalls:Confusing helicase with topoisomerase; the latter relieves torsional stress but does not separate base pairs directly.

Final Answer:Helicase