- A Cleaving caspase substrates directly to dismantle the nuclear envelope and trigger apoptosis
- B Binding E2F transcription factors, blocking S phase entry until phosphorylated by Cyclin D/Cdk4
- C Anchoring kinetochores to spindle microtubules to satisfy the metaphase checkpoint
- D Recruiting nucleotide excision repair enzymes to sites of UV-induced DNA damage
Correct answer: B. Binding E2F transcription factors, blocking S phase entry until phosphorylated by Cyclin D/Cdk4
Explanation: Rb protein sequesters E2F transcription factors. Cyclin D/Cdk4 (and Cdk6) phosphorylate Rb, releasing E2F to activate S-phase genes. This is the critical G1 to S transition.
Concept context
Mitosis and meiosis: how cells divide for growth, repair, and reproduction.