Actin binding sites are located on

Options

A. troponin
B. tropomyosin
C. meromyosin
D. bith (b) and (c).

Explanation

### Step-by-Step Solution:

1. **Understanding Muscle Structure**:
- Striated muscles, also known as skeletal muscles, are characterized by their striped appearance when viewed under a microscope. This is due to the arrangement of two main contractile proteins: actin and myosin.

2. **Identifying the Proteins**:
- Actin forms the thin filaments of muscle fibers, while myosin forms the thick filaments. The interaction between these two proteins is crucial for muscle contraction.

3. **Role of Actin and Myosin**:
- For muscle contraction to occur, actin and myosin must bind together to form cross-bridges. This binding is essential for the sarcomere (the functional unit of muscle) to shorten, leading to muscle contraction.

4. **Analyzing the Options**:
- The question provides three options: troponin, tropomyosin, and meromyosin.
- **Troponin**: This protein is associated with actin and is distributed along the actin filaments. However, it does not have binding sites for actin itself.
- **Tropomyosin**: This protein runs along the length of actin filaments and also does not have binding sites for actin, as it is part of the actin structure.
- **Meromyosin**: This is a component of myosin. It consists of heavy meromyosin and light meromyosin. The heavy meromyosin has an active site that binds to actin.

5. **Conclusion**:
- The binding sites for actin are located on the heavy meromyosin (the heavy head of the myosin protein). Therefore, the correct answer is **meromyosin**.

### Final Answer:
The actin binding sites are located on **meromyosin**.

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