In DNA replication, what is the primary function of DNA helicase?

• A. It synthesizes new DNA strands by adding nucleotides to the $3^{\prime }$ end of a primer.
• B. It unwinds the parental DNA double helix by breaking hydrogen bonds at the replication fork.
• C. It relieves supercoiling ahead of the replication fork by introducing transient breaks in DNA.
• D. It joins Okazaki fragments on the lagging strand by forming phosphodiester bonds.

Answer: (B)

Verified step by step guidance

1. Understand the role of DNA helicase in the context of DNA replication, which involves the separation of the two strands of the DNA double helix.
2. Recall that DNA helicase functions by breaking the hydrogen bonds between complementary base pairs, allowing the two strands to unwind and separate.
3. Recognize that this unwinding creates the replication fork, a critical structure where DNA synthesis occurs.
4. Differentiate DNA helicase's function from other enzymes involved in replication, such as DNA polymerase (which synthesizes new strands), topoisomerase (which relieves supercoiling), and DNA ligase (which joins Okazaki fragments).
5. Conclude that the primary function of DNA helicase is to unwind the parental DNA double helix by breaking hydrogen bonds at the replication fork, enabling the replication machinery to access single-stranded DNA templates.