Q.5
Which checkpoint in the cell cycle ensures that DNA is undamaged and ready for replication?
- G1 Cell Cycle Checkpoint (Restriction Point / START):
- Operates near the transition between $\text{G}_1$ and S phase to verify that genomic DNA is intact, nutrient supplies are sufficient, and cell size is appropriate before committing the cell to irreversible DNA replication.
- If DNA damage is detected, sensor kinases (ATM/ATR) activate p53, which induces transcription of Cdk inhibitor p21 ($CIP1/WAF1$). This arrests the cell cycle in $\text{G}_1$ to prevent replication of damaged DNA templates.
Correct option: (1) G1 checkpoint
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