Which statement describes a step in DNA replication?

• A. Topoisomerase adds nucleotides to the growing DNA strand.
• B. RNA polymerase synthesizes a new DNA strand.
• C. Helicase unwinds the DNA double helix.
• D. DNA ligase breaks the hydrogen bonds between bases.

Answer: (C)

Verified step by step guidance

1. Understand the process of DNA replication, which involves unwinding the DNA double helix, synthesizing new strands, and joining fragments.
2. Identify the role of helicase in DNA replication. Helicase is an enzyme that unwinds the DNA double helix by breaking the hydrogen bonds between the base pairs, allowing the two strands to separate.
3. Recognize that topoisomerase is involved in relieving the tension created by the unwinding of the DNA helix, but it does not add nucleotides.
4. Note that RNA polymerase is not involved in DNA replication; it is responsible for synthesizing RNA during transcription.
5. Understand that DNA ligase is responsible for joining Okazaki fragments on the lagging strand, not breaking hydrogen bonds.