During DNA replication, which enzyme is primarily responsible for unwinding ("unzipping") the DNA double helix at the replication fork?

• A. DNA helicase
• B. DNA ligase
• C. Primase
• D. DNA polymerase III

Answer: (A)

Verified step by step guidance

1. Understand the process of DNA replication, which involves unwinding the double helix, synthesizing new strands, and joining fragments.
2. Identify the role of each enzyme listed: DNA helicase, DNA ligase, primase, and DNA polymerase III.
3. Recall that DNA helicase is the enzyme responsible for breaking the hydrogen bonds between complementary base pairs, effectively unwinding or "unzipping" the DNA double helix at the replication fork.
4. Recognize that DNA ligase joins Okazaki fragments on the lagging strand, primase synthesizes RNA primers, and DNA polymerase III extends the new DNA strand.
5. Conclude that the enzyme primarily responsible for unwinding the DNA double helix is DNA helicase.