At which cell cycle checkpoint is the cell cycle halted if the cell's DNA is damaged?

Options

A. `G_(1) - S`
B. `S-G_(2)`
C. `G_(2)-M`
D. `G_(0)-G_(1)`

Answer

To determine at which cell cycle checkpoint the cell cycle is halted if the cell's DNA is damaged, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Cell Cycle Phases**: The cell cycle consists of several phases: G1 (Gap 1), S (Synthesis), G2 (Gap 2), and M (Mitosis).

2. **Identify the Checkpoints**: There are three main checkpoints in the cell cycle:
- **G1/S Checkpoint**: This checkpoint occurs at the transition from G1 to S phase.
- **G2/M Checkpoint**: This checkpoint occurs at the transition from G2 to M phase.
- **M Checkpoint**: This checkpoint occurs during the M phase, ensuring that all chromosomes are properly aligned before division.

3. **Recognize the Role of Checkpoints**: Checkpoints are critical control mechanisms that ensure the integrity of the cell's DNA and the proper progression of the cell cycle. If any damage is detected, the cell cycle can be halted to prevent the propagation of damaged DNA.

4. **Focus on DNA Damage**: When DNA is damaged, the cell needs to halt the cycle to repair the damage. The first checkpoint (G1/S) is primarily responsible for assessing the cell's environment and DNA integrity before the cell commits to DNA replication.

5. **Conclusion**: If the cell's DNA is damaged, the cell cycle is halted at the **G1/S checkpoint**. This is the point where the cell assesses whether it is ready to proceed to the S phase for DNA synthesis.

### Final Answer:
The cell cycle is halted at the **G1/S checkpoint** if the cell's DNA is damaged.

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