The 'restriction point' occurs here:

Options

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

Answer

**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.

2. **Identifying the Restriction Point:**
The restriction point, often denoted as 'R', is a crucial checkpoint in the cell cycle. It is the point at which the cell decides whether to continue with the cell cycle or enter a resting phase.

3. **Locating the Restriction Point:**
The restriction point occurs at the end of the G1 phase, just before the cell transitions into the S phase. At this point, the cell has completed its preparations for DNA synthesis.

4. **Significance of the Restriction Point:**
After the restriction point, the cell is committed to proceeding through the rest of the cell cycle, regardless of external signals or growth factors. This means that once the cell passes this point, it will continue to divide.

5. **Conclusion:**
Therefore, the restriction point occurs at the end of the G1 phase, serving as a critical checkpoint before the cell enters the S phase.

**Final Answer:**
The restriction point occurs at the end of the G1 phase of the cell cycle.

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