Passage through which checkpoint is the step which commits the cell to proceed through to mitosis and cell division?

Options

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

Answer

To determine the checkpoint that commits the cell to proceed through mitosis and cell division, we need to analyze the cell cycle and the specific checkpoints involved.

### Step-by-Step Solution:

1. **Understanding the Cell Cycle**: The cell cycle consists of several phases: G1 (Gap 1), S (Synthesis), G2 (Gap 2), and M (Mitosis). Each phase has specific functions and checkpoints to ensure proper cell division.

2. **Identifying the Checkpoints**: There are three main checkpoints in the cell cycle:
- **G1 Checkpoint**: This checkpoint occurs at the end of the G1 phase before the cell enters the S phase.
- **G2 Checkpoint**: This occurs at the end of the G2 phase before the cell enters the M phase.
- **M Checkpoint**: This occurs during the M phase, ensuring that all chromosomes are properly aligned before division.

3. **Focus on the G1 to S Checkpoint**: The G1 to S checkpoint is crucial because it is the first point where the cell decides whether to continue with the cell cycle. If the cell passes this checkpoint, it commits to DNA replication and subsequently to cell division.

4. **Role of CDK Complexes**: Cyclin-dependent kinases (CDKs) are activated at the G1 checkpoint. They provide the necessary signals (known as the Go-Ahead signal) that allow the cell to proceed to the S phase.

5. **Conclusion**: The checkpoint that commits the cell to proceed through mitosis and cell division is the **G1 to S checkpoint**.

### Final Answer:
The checkpoint that commits the cell to proceed through mitosis and cell division is the **G1 to S checkpoint**.

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