How many checkpoints in a cell cycle?

Options

A. 3
B. 4
C. 5
D. 6

Answer

To answer the question "How many checkpoints are in a cell cycle?", we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Cell Cycle**: The cell cycle consists of several phases, including G1 (Gap 1), S (Synthesis), G2 (Gap 2), and M (Mitosis). During these phases, the cell undergoes various processes to prepare for division.

2. **Identifying Checkpoints**:
- **First Checkpoint (G1/S Checkpoint)**: This checkpoint occurs at the transition from the G1 phase to the S phase. It checks for DNA damage and ensures that the cell is ready for DNA replication.
- **Second Checkpoint (G2/M Checkpoint)**: This checkpoint occurs at the transition from the G2 phase to the M phase. It checks for DNA damage after replication and ensures that all DNA is replicated correctly before the cell enters mitosis.
- **Third Checkpoint (M Checkpoint)**: This checkpoint occurs during the M phase, specifically from metaphase to anaphase. It ensures that all chromosomes are properly attached to the spindle apparatus before the cell proceeds with division.

3. **Counting the Checkpoints**: Based on the descriptions above, we can identify that there are a total of **three checkpoints** in the cell cycle:
- G1/S Checkpoint
- G2/M Checkpoint
- M Checkpoint

4. **Conclusion**: Therefore, the answer to the question is that there are **three checkpoints in a cell cycle**.

### Final Answer:
There are three checkpoints in a cell cycle.

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