The regulatory protein of skeletal muscles whose filaments run close to the F - actin throughout its length is
(a) Troponin T
(b) Troponin C
(c) Troponin I
(d) Tropomyosin

Options

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

Answer

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

### Step-by-Step Solution:

1. **Understand the Components**:
- We need to identify the regulatory proteins associated with skeletal muscle contraction. The main proteins involved are actin (specifically F-actin), myosin, and regulatory proteins like troponin and tropomyosin.

2. **Identify F-actin**:
- F-actin is a filamentous form of actin that is crucial for muscle contraction. It is composed of G-actin monomers.

3. **Recognize the Role of Regulatory Proteins**:
- Regulatory proteins control the interaction between actin and myosin. The troponin complex (which includes Troponin T, Troponin C, and Troponin I) is involved in this regulation but does not run continuously along the length of the F-actin.

4. **Focus on Tropomyosin**:
- Tropomyosin is another regulatory protein that runs along the length of the F-actin. It covers the binding sites on actin, preventing myosin from binding to actin when the muscle is relaxed.

5. **Evaluate the Options**:
- (a) Troponin T - part of the troponin complex, not continuous along F-actin.
- (b) Troponin C - also part of the troponin complex, not continuous.
- (c) Troponin I - part of the troponin complex, not continuous.
- (d) Tropomyosin - runs along the length of F-actin and regulates the binding of myosin.

6. **Select the Correct Answer**:
- Based on the information, the correct answer is (d) Tropomyosin, as it is the regulatory protein that runs close to F-actin throughout its length.

### Final Answer:
(d) Tropomyosin