Which is used as mitotic spindle poison

Options

A. `Ca^(2+)`
B. `Mg^(2+)`
C. Tubulin
D. Colchincine

Answer

To determine which substance is used as a mitotic spindle poison, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Mitotic Spindle**:
- The mitotic spindle, also known as the spindle apparatus, is a structure that segregates chromosomes during cell division (mitosis). It is crucial for ensuring that each daughter cell receives an equal and accurate set of chromosomes.

2. **Identify the Role of Spindle Fibers**:
- Spindle fibers are formed from proteins called tubulin. These fibers attach to the centromeres of chromosomes and help pull them apart into the two daughter cells during mitosis.

3. **Define Mitotic Spindle Poison**:
- A mitotic spindle poison is a substance that disrupts the formation or function of the spindle fibers, thereby inhibiting proper chromosome segregation during cell division.

4. **Evaluate the Options**:
- **Option A: Ca2+ (Calcium ions)** - Not a mitotic spindle poison; it is involved in various cellular processes but does not inhibit spindle fiber formation.
- **Option B: Mg2+ (Magnesium ions)** - Similar to calcium, magnesium is important for cellular functions but does not act as a spindle poison.
- **Option C: Tubulin** - This is the protein that makes up the spindle fibers, so it cannot be a poison that inhibits spindle formation.
- **Option D: Colchicine** - This is known to inhibit the polymerization of tubulin, preventing the formation of spindle fibers. Therefore, it acts as a mitotic spindle poison.

5. **Conclusion**:
- Based on the evaluation of the options, the correct answer is **Colchicine** (Option D), as it prevents the formation of spindle fibers necessary for mitosis.

### Final Answer:
**Colchicine is used as a mitotic spindle poison.**