Actin fiber is present in

Options

A. Cilia
B. Flagella
C. Carbohydrates
D. Microfilaments

Answer

### Step-by-Step Solution:

1. **Understanding Actin**:
- Actin is a protein that plays a crucial role in various cellular functions, including muscle contraction, cell movement, and maintaining cell shape.

2. **Location of Actin**:
- Actin is present in all types of cells, but it is particularly abundant in muscle cells. This is because actin filaments are essential for muscle contraction.

3. **Types of Actin**:
- Actin exists in two forms:
- **G-actin (Globular actin)**: This is the monomeric form of actin, which is a globular protein.
- **F-actin (Filamentous actin)**: This is the polymerized form of G-actin, where multiple G-actin monomers come together to form long filaments.

4. **Function of Actin**:
- The polymerization of G-actin into F-actin leads to the formation of microfilaments, which are part of the cytoskeleton. These microfilaments are involved in various cellular processes, including providing structural support and enabling movement.

5. **Conclusion**:
- Therefore, actin fibers are present in microfilaments, which are found in all cells, but are particularly abundant in muscle cells.

### Final Answer:
Actin fibers are present in microfilaments, especially abundant in muscle cells.

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