Among the following proteins : Tropomyosin, Troponin, F-actin, Meromyosin How many are present in l-band and H-zone respectively?

Options

A. 3, 1
B. 3,2
C. 4,1
D. 1,3

Answer

To solve the question regarding the presence of proteins in the I-band and H-zone of a sarcomere, we will analyze each protein and its association with these regions.

### Step-by-Step Solution:

1. **Understand the Structure of Sarcomere**:
- The sarcomere is the basic structural and functional unit of muscle contraction. It contains thick and thin filaments.
- Thick filaments are primarily made of myosin, while thin filaments are made of actin.

2. **Identify the Proteins**:
- **Tropomyosin**: A protein that binds to actin and is part of the thin filament.
- **Troponin**: A complex of proteins that also binds to actin and is involved in muscle contraction.
- **F-actin**: Filamentous actin, which is the main component of the thin filament.
- **Meromyosin**: A fragment of myosin that constitutes the thick filament.

3. **Determine the Components of the I-band**:
- The I-band consists solely of thin filaments (actin). Therefore, all proteins associated with actin will be found here.
- The proteins present in the I-band are:
- Tropomyosin
- Troponin
- F-actin
- **Total in I-band**: 3 proteins.

4. **Determine the Components of the H-zone**:
- The H-zone is the region of the sarcomere that contains only thick filaments (myosin) and does not overlap with thin filaments.
- The only protein present in the H-zone from the list is:
- Meromyosin
- **Total in H-zone**: 1 protein.

5. **Final Summary**:
- In the I-band, there are 3 proteins (Tropomyosin, Troponin, F-actin).
- In the H-zone, there is 1 protein (Meromyosin).

### Conclusion:
- The answer to the question is:
- **I-band**: 3 proteins
- **H-zone**: 1 protein