When cell has stalled DNA replication fork , which checkpoint should be predominantly activated

Options

A. `G_(1)//S`
B. `G_(2)//M`
C. M
D. Both `G_(2)//M and M`

Answer

To determine which checkpoint is predominantly activated when a cell has a stalled DNA replication fork, 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).
- Each phase has specific functions related to cell growth and division.

2. **Identify the Role of Each Phase**:
- **G1 Phase**: This phase focuses on cell growth and preparation for DNA synthesis.
- **S Phase**: This is where DNA replication occurs, and genetic material is synthesized.
- **G2 Phase**: This phase involves further growth and preparation for mitosis, ensuring all components are ready for division.
- **M Phase**: This is the phase where actual cell division occurs.

3. **Recognize the Impact of a Stalled DNA Replication Fork**:
- A stalled DNA replication fork indicates that the process of DNA synthesis is interrupted.
- This directly affects the S phase, as it is responsible for DNA replication.

4. **Determine the Checkpoints**:
- The cell cycle has specific checkpoints to monitor the integrity of the DNA and the cell's readiness to proceed to the next phase.
- The G1 checkpoint assesses the cell's size and DNA integrity before entering the S phase.
- The G2 checkpoint ensures that DNA has been accurately replicated and checks for any damage before the cell enters mitosis.

5. **Identify the Predominant Checkpoint Activated**:
- Since the stalled DNA replication fork indicates an issue during the S phase, the G1/S checkpoint will be activated to prevent the cell from proceeding with division until the issue is resolved.
- This checkpoint will ensure that any errors or damages are addressed before the cell can continue to the G2 phase and ultimately to mitosis.

### Conclusion:
The predominantly activated checkpoint when a cell has a stalled DNA replication fork is the **G1/S checkpoint**.

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