Which of the following statements regarding the structure of contractile proteins are correct ?
I. Each actin filaments is made up of two ' F ' actins, which are wound helically around each other.
II. Two types of troponins are distributed at regular intervals on the tropomyosin .
III. The globular head of meromyosin has binding sites for ATP and troponins.
IV myosin is a structure proteins which also has enzymatic activity.

Options

A. II, III and IV
B. I and IV
C. I,II and III
D. II and IV

Answer

To determine which statements regarding the structure of contractile proteins are correct, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement I**: "Each actin filament is made up of two 'F' actins, which are wound helically around each other."
- **Analysis**: This statement is correct. Actin filaments (F-actin) are indeed composed of two strands of filamentous actin that are wound together in a helical structure.

2. **Statement II**: "Two types of troponins are distributed at regular intervals on the tropomyosin."
- **Analysis**: This statement is incorrect. There are three types of troponin (Troponin C, Troponin I, and Troponin T) that are associated with tropomyosin, not two.

3. **Statement III**: "The globular head of meromyosin has binding sites for ATP and troponins."
- **Analysis**: This statement is partially correct. The globular head of myosin (not specifically meromyosin) does have binding sites for ATP, but it does not have binding sites for troponin. Troponin and tropomyosin are associated with actin filaments, not myosin heads.

4. **Statement IV**: "Myosin is a structural protein which also has enzymatic activity."
- **Analysis**: This statement is correct. Myosin is indeed a structural protein and has ATPase activity, which is an enzymatic function.

### Conclusion:
Based on the analysis:
- **Correct Statements**: I and IV
- **Incorrect Statements**: II and III

The correct answer is that statements I and IV are correct.

### Final Answer:
The correct statements regarding the structure of contractile proteins are I and IV.