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

• A. It joins Okazaki fragments together by forming phosphodiester bonds.
• B. It synthesizes new DNA strands by adding nucleotides in the $5\prime \to 3\prime$ direction.
• C. It unwinds the parental DNA double helix by breaking hydrogen bonds between complementary bases.
• D. It removes RNA primers from the lagging strand and replaces them with DNA.

Answer: (C)

Verified step by step guidance

1. Understand the role of DNA helicase in DNA replication, which occurs at the replication fork where the double-stranded DNA is separated into single strands to serve as templates.
2. Recall that DNA helicase functions by breaking the hydrogen bonds between complementary base pairs, effectively unwinding the parental DNA double helix.
3. Recognize that this unwinding is essential because it allows other enzymes, such as DNA polymerase, to access the single-stranded DNA and synthesize new strands.
4. Differentiate the function of DNA helicase from other enzymes: for example, DNA ligase joins Okazaki fragments, DNA polymerase synthesizes new DNA strands in the 5' to 3' direction, and RNase H removes RNA primers.
5. Conclude that the primary function of DNA helicase at the replication fork is to unwind the parental DNA double helix by breaking hydrogen bonds between complementary bases.