Ribonuclease, a mitotic poison, inhibits cell cycle in:-

Options

A. Interphase
B. Prophase
C. Metaphase
D. Anaphase

Answer

To solve the question regarding Ribonuclease, a mitotic poison, and its effect on the cell cycle, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Ribonuclease**: Ribonuclease is an enzyme that catalyzes the degradation of RNA. It acts by breaking down RNA molecules, which are essential for various cellular processes, including protein synthesis.

**Hint**: Consider the role of RNA in the cell cycle and how its degradation might affect cell division.

2. **Identifying the Cell Cycle Phases**: The cell cycle consists of several phases: Interphase (which includes G1, S, and G2 phases) and the Mitotic phase (which includes prophase, metaphase, anaphase, and telophase).

**Hint**: Recall the different phases of the cell cycle and their significance in cell division.

3. **Analyzing Interphase**: During the G1 phase of Interphase, RNA synthesis occurs, which is crucial for the cell to prepare for DNA replication and subsequent cell division. If Ribonuclease degrades RNA during this phase, it would inhibit the necessary RNA synthesis.

**Hint**: Think about what happens in G1 phase and how RNA is involved in preparing the cell for division.

4. **Evaluating Other Phases**:
- **Prophase**: This phase involves chromatin condensation and does not primarily rely on RNA synthesis.
- **Metaphase**: Chromosomes align at the equator, and RNA synthesis is not a key process here.
- **Anaphase**: Sister chromatids separate and move towards the poles, again not dependent on RNA synthesis.

**Hint**: Compare the role of RNA in Interphase versus the mitotic phases.

5. **Conclusion**: Since Ribonuclease inhibits RNA synthesis, it will primarily affect the G1 phase of Interphase, leading to an overall inhibition of the cell cycle.

**Final Answer**: Ribonuclease inhibits the cell cycle in **Interphase** (Option 1).

### Summary of the Answer:
The correct answer is **Interphase**, as Ribonuclease degrades RNA, which is essential for the processes occurring in the G1 phase of the cell cycle.