During DNA replication, what is the primary role of DNA helicase?

• A. It unwinds the DNA double helix by breaking hydrogen bonds between complementary base pairs at the replication fork.
• B. It synthesizes short RNA primers to provide a 3′-OH group for DNA polymerase to begin elongation.
• C. It joins Okazaki fragments together by sealing nicks in the sugar-phosphate backbone.
• D. It adds nucleotides to the growing DNA strand in the 5′ to 3′ direction.

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the process of DNA replication, which involves unwinding the double helix, synthesizing RNA primers, elongating new DNA strands, and joining fragments on the lagging strand.
2. Step 2: Identify the specific function of DNA helicase, which is to separate the two strands of the DNA double helix by breaking the hydrogen bonds between complementary base pairs, creating the replication fork.
3. Step 3: Recognize that this unwinding is essential because it allows other enzymes, such as DNA polymerase, to access the single-stranded DNA templates for replication.
4. Step 4: Differentiate DNA helicase's role from other enzymes: primase synthesizes RNA primers, DNA ligase joins Okazaki fragments, and DNA polymerase adds nucleotides to the growing strand.
5. Step 5: Conclude that the primary role of DNA helicase is to unwind the DNA double helix at the replication fork, enabling the replication machinery to function properly.