Which one is not a fibrillar protein

Options

A. Keratin
B. Collagen
C. Albumin
D. Elastin.

Answer

To determine which of the given options is not a fibrillar protein, we will analyze each option based on the characteristics of fibrillar (or fibrous) proteins.

### Step-by-Step Solution:

1. **Understanding Fibrillar Proteins**:
- Fibrillar proteins, also known as fibrous proteins, consist of long, parallel polypeptide chains.
- They typically form helical structures or pleated sheets and are insoluble in water.
- These proteins primarily provide structural support and mechanical functions in the body.

2. **Analyzing the Options**:
- **Keratin**:
- Keratin is a fibrous protein found in hair, nails, and the outer layer of skin.
- It is insoluble in water and provides structural support.
- Therefore, keratin is a fibrillar protein.
- **Collagen**:
- Collagen is the most abundant protein in the body and is a major component of connective tissues, including bones and cartilage.
- It also has a fibrous structure and is insoluble in water.
- Hence, collagen is a fibrillar protein.
- **Albumin**:
- Albumin is a globular protein, not a fibrous protein.
- It is soluble in water and plays a crucial role in maintaining osmotic pressure and transporting substances in the blood.
- Therefore, albumin is not a fibrillar protein.
- **Elastin**:
- Elastin is another fibrous protein that provides elasticity to tissues such as skin and blood vessels.
- It is insoluble in water and contributes to structural functions.
- Thus, elastin is a fibrillar protein.

3. **Conclusion**:
- Among the options provided, **albumin** is the only one that is not a fibrillar protein. It is a globular protein, while keratin, collagen, and elastin are all fibrillar proteins.

### Final Answer:
**Albumin** is not a fibrillar protein.