The regulatory protein of skeletal muscles whose filaments run close to the F - actin throughout its length is

Options

A. Troponin T
B. Troponin C
C. Troponin I
D. Tropomyosin

Answer

To solve the question regarding the regulatory protein of skeletal muscles whose filaments run close to the F-actin throughout its length, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Components of Muscle Filaments**:
- Skeletal muscles are composed of two main types of filaments: thick filaments (myosin) and thin filaments (actin).
- Thin filaments are primarily made up of actin, which exists in two forms: G-actin (globular actin) and F-actin (filamentous actin).

2. **Identify the Structure of F-actin**:
- F-actin is a polymer made up of G-actin monomers. These G-actin monomers polymerize to form long helical structures known as F-actin.

3. **Recognize the Role of Tropomyosin**:
- Tropomyosin is a regulatory protein that runs along the length of the F-actin filaments. It lies in the grooves of the F-actin helix, effectively running parallel to it.

4. **Consider Other Regulatory Proteins**:
- Troponin is another regulatory protein associated with tropomyosin, but it does not run along the length of F-actin. Instead, it binds to tropomyosin and helps regulate muscle contraction by interacting with calcium ions.

5. **Conclusion**:
- Since the question specifically asks for the protein that runs close to F-actin throughout its length, the correct answer is **Tropomyosin**.

### Final Answer:
The regulatory protein of skeletal muscles whose filaments run close to the F-actin throughout its length is **Tropomyosin**.

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