Listed below are certain proteins. Which of them are the only structural proteins ?
(i) Collagen (ii) Trypsion
(iii) Keratin (iv) Actin
(v) Albumin (vi) Tubulin

Options

A. (i),(iii),(iv)
B. (ii),(iv),(v), (vi)
C. (i),(iii),(vi)
D. (i),(iii), (iv),(v),(vi)

Answer

To determine which of the listed proteins are structural proteins, we need to analyze each protein based on its function and characteristics.

1. **Collagen**:
- Collagen is a well-known structural protein. It is a major component of connective tissues, such as tendons, ligaments, and skin. It provides strength and support to these tissues.
- **Conclusion**: Collagen is a structural protein.

2. **Trypsin**:
- Trypsin is an enzyme that plays a crucial role in digestion by breaking down proteins into smaller peptides. It does not serve a structural role in cells or tissues.
- **Conclusion**: Trypsin is not a structural protein.

3. **Keratin**:
- Keratin is another structural protein. It is found in hair, nails, and the outer layer of skin. It provides protection and structural integrity to these tissues.
- **Conclusion**: Keratin is a structural protein.

4. **Actin**:
- Actin is a globular protein that forms microfilaments and is involved in various cellular processes, including muscle contraction and cell movement. While it plays a role in the cytoskeleton, it is not classified as a structural protein in the same sense as collagen or keratin.
- **Conclusion**: Actin is not a structural protein.

5. **Albumin**:
- Albumin is a carrier protein that helps transport various substances in the blood, such as fatty acids and hormones. It does not have a structural role.
- **Conclusion**: Albumin is not a structural protein.

6. **Tubulin**:
- Tubulin is a protein that polymerizes to form microtubules, which are part of the cytoskeleton. Microtubules provide structural support and shape to cells, making tubulin a structural protein.
- **Conclusion**: Tubulin is a structural protein.

### Summary of Structural Proteins:
- **Structural Proteins**: Collagen, Keratin, Tubulin
- **Non-Structural Proteins**: Trypsin, Actin, Albumin

### Final Answer:
The proteins that are only structural proteins from the list are:
- (i) Collagen
- (iii) Keratin
- (vi) Tubulin