NEET · BiologyHard
During the cell cycle, the transition from G1 to S phase is tightly regulated by the E2F transcription factor. What is the mechanism by which the Retinoblastoma protein (pRb) inhibits this transition?
- A.It promotes the degradation of Cyclin D
- B.It binds to E2F and prevents it from activating transcription of S-phase genes
- C.It phosphorylates the CDK4/6 complex to inhibit its activity
- D.It directly binds to the origin of replication to block DNA polymerase
Show correct answer & step-by-step solution
Correct answer: B — It binds to E2F and prevents it from activating transcription of S-phase genes
Solution
- In G1 phase, pRb is in a hypophosphorylated state.
- Hypophosphorylated pRb binds to E2F transcription factors.
- This binding prevents E2F from activating the transcription of genes necessary for DNA replication.
- Phosphorylation of pRb by Cyclin-CDK complexes releases E2F, allowing S-phase progression.
- Hence the answer is (B).
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