A Levels Biology (9700)•9700/11/M/J/21
Explanation
DNA Uncoiling Essential for Replication in Interphase
Steps:
- Cell cycle includes interphase (G1, S, G2) for preparation and mitosis for division.
- DNA double helix uncoils and separates during S phase of interphase for replication.
- Preventing uncoiling blocks replication, halting tumor cell proliferation.
- Mitotic stages involve already replicated, condensed chromosomes, not uncoiling.
Why B is correct:
- Interphase's S phase requires DNA helicase to unwind the double helix for semiconservative replication, per Watson-Crick model.
Why the others are wrong:
- A. Anaphase separates sister chromatids; DNA replication is complete.
- C. Metaphase aligns chromosomes at equator; no DNA uncoiling occurs.
- D. Prophase condenses chromatin into chromosomes; uncoiling is unnecessary.
Final answer: B
Topic: Replication and division of nuclei and cells
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