During DNA replication, which enzyme unwinds ("unzips") the parental DNA double helix at the replication fork?

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

Answer: (D)

Verified step by step guidance

1. Understand the role of each enzyme listed in the problem during DNA replication.
2. Recall that DNA replication begins at the replication fork, where the double helix must be separated into two single strands.
3. Identify the enzyme responsible for unwinding or "unzipping" the parental DNA double helix to expose the single strands for replication.
4. Recognize that DNA helicase is the enzyme that breaks the hydrogen bonds between base pairs, effectively unwinding the DNA.
5. Confirm that other enzymes like primase, DNA ligase, and DNA polymerase III have different roles: primase synthesizes RNA primers, DNA ligase joins Okazaki fragments, and DNA polymerase III synthesizes new DNA strands.