What is the role of helicase at the replication fork?

• A. Untwists the double helix and separates the two strands.
• B. Synthesizes the new DNA strand by adding nucleotides.
• C. Ligates Okazaki fragments.
• D. Stabilizes single-stranded DNA.

Answer: (A)

The main idea is that helicase is the motor that unwinds the DNA at the replication fork. It uses energy from ATP to break the hydrogen bonds between base pairs, pulling the two strands apart and creating the fork so that each template becomes accessible for copying. This unwinding sets the stage for the DNA polymerases to synthesize new strands, with single-strand binding proteins stabilizing the exposed templates to keep them from reannealing. While helicase does the opening, other enzymes handle primer placement, synthesis, handling of Okazaki fragments, and joining fragments. So, the essential role of helicase is to untwist and separate the double helix, enabling replication to proceed.