Globular protein of `~6kDa` consisting of 51 amino acids arranged in two polypeptide chains held by disulphide bridge is

Options

A. Insulin
B. Fibrinogen
C. Glucagon
D. Keratin

Answer

To solve the question regarding the globular protein of approximately 6 kDa consisting of 51 amino acids arranged in two polypeptide chains held by disulfide bridges, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Characteristics of the Protein:**
- The protein is globular, which typically means it has a compact, spherical shape.
- It has a molecular weight of approximately 6 kDa (kilodaltons).
- It consists of 51 amino acids.
- It is made up of two polypeptide chains that are linked by disulfide bridges.

2. **Identifying Possible Proteins:**
- The options provided are insulin, fibrinogen, glucagon, and keratin.
- We need to analyze each of these proteins based on the characteristics mentioned.

3. **Analyzing Insulin:**
- Insulin is a well-known hormone that regulates blood sugar levels.
- It consists of two chains: the A chain (21 amino acids) and the B chain (30 amino acids).
- Together, these chains total 51 amino acids (21 + 30 = 51).
- Insulin has a molecular weight of approximately 6 kDa.
- The two chains are connected by disulfide bridges.

4. **Analyzing Other Options:**
- **Fibrinogen:** This is a larger protein involved in blood clotting and does not fit the weight or amino acid count.
- **Glucagon:** This hormone is also larger than insulin and does not match the specified characteristics.
- **Keratin:** This is a fibrous protein and does not have the globular structure or the specified molecular weight.

5. **Conclusion:**
- Based on the analysis, the only protein that fits all the criteria (globular structure, 6 kDa weight, 51 amino acids, and two polypeptide chains linked by disulfide bridges) is **insulin**.

### Final Answer:
The globular protein of approximately 6 kDa consisting of 51 amino acids arranged in two polypeptide chains held by disulfide bridges is **insulin**.

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