In DNA replication, what is the primary role of helicase at the replication fork?

• A. It relieves supercoiling ahead of the replication fork by cutting and rejoining DNA strands.
• B. It seals nicks in the sugar-phosphate backbone by forming phosphodiester bonds between Okazaki fragments.
• C. It synthesizes new DNA strands by adding nucleotides to the 3′ end of a primer.
• D. It unwinds the parental double helix by breaking hydrogen bonds between complementary bases.

Answer: (D)

Verified step by step guidance

1. Understand the context of DNA replication, which involves unwinding the double helix and synthesizing new strands.
2. Identify the replication fork as the site where the DNA double helix is separated into two single strands to serve as templates.
3. Recognize that helicase is an enzyme whose primary function is to unwind the parental DNA double helix.
4. Know that helicase achieves this by breaking the hydrogen bonds between complementary base pairs, separating the two strands.
5. Distinguish helicase's role from other enzymes: topoisomerase relieves supercoiling, DNA ligase seals nicks, and DNA polymerase synthesizes new DNA.