Which statement correctly describes the action of helicase?

Which statement correctly describes the action of helicase?

• A. It seals nicks in the DNA backbone.
• B. It untwists the double helix at replication forks into two strands.
• C. It synthesizes DNA.
• D. It binds ligases to Okazaki fragments.

Answer: (B)

Helicase’s job is to unwind the DNA double helix at the replication fork, using energy from ATP to separate the two strands so replication can proceed. This action literally untwists and opens the DNA, creating the two templates for synthesis. That’s why this statement is the best fit: it describes the unwinding that helicase performs. Other enzymes do different tasks—DNA ligase seals nicks and joins fragments, while DNA polymerase synthesizes new DNA—so they don’t describe helicase’s function.

Helicase’s job is to unwind the DNA double helix at the replication fork, using energy from ATP to separate the two strands so replication can proceed. This action literally untwists and opens the DNA, creating the two templates for synthesis. That’s why this statement is the best fit: it describes the unwinding that helicase performs. Other enzymes do different tasks—DNA ligase seals nicks and joins fragments, while DNA polymerase synthesizes new DNA—so they don’t describe helicase’s function.