# DBT JRF 2022 — Question 40

Exam: DBT JRF 2022 · Section: B · Topic: Cell Biology › Cell Cycle Checkpoints · Difficulty: Medium

## Question

Which one of the following is NOT a major checkpoint in the cell division cycle of eukaryotic cell?

## Options

- **A.** Beginning of S-phase
- **B.** Transition from S to G2 phase
- **C.** Transition from G2 to M phase
- **D.** Transition from Metaphase to Anaphase during Mitosis

## Answer

Option B

## Explanation

Major cell cycle checkpoints in eukaryotes: The three major checkpoints: 1. G1/S checkpoint (Restriction point in G1): Checks for DNA damage, adequate cell size, and growth factor signals before committing to DNA replication. Key proteins: p53, Rb, CDK4/6-cyclin D. 2. G2/M checkpoint: Ensures all DNA has been replicated correctly and any damage is repaired before mitosis. Key proteins: CDK1-cyclin B (MPF), ATM/ATR. 3. Spindle Assembly Checkpoint (SAC, M phase): Ensures all kinetochores are properly attached to spindle microtubules before anaphase. Key proteins: Mad2, BubR1. The S-to-G2 transition is NOT a recognised major checkpoint in the classical cell cycle model. Answer: G1/S, G2/M, and Spindle Assembly Checkpoint (metaphase→anaphase) are the three major checkpoints.

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