Insulin has two polypeptide chains. These polypeptide chains are held together by

Options

A. Peroxy linkage
B. Disulphide linkage
C. Diazo bonding
D. H-bonding

Answer

To answer the question, "Insulin has two polypeptide chains. These polypeptide chains are held together by," we need to analyze the structure of insulin and the types of bonds that can hold polypeptide chains together.

### Step-by-Step Solution:

1. **Understanding Insulin Structure**:
- Insulin is a protein hormone that consists of two polypeptide chains known as the A chain and the B chain.

2. **Identifying the Linkage**:
- The A chain and B chain of insulin are not just floating independently; they are connected to each other.

3. **Types of Linkages**:
- Proteins can be held together by various types of bonds, including hydrogen bonds, ionic bonds, and disulfide bonds.

4. **Disulfide Linkages**:
- In the case of insulin, the two polypeptide chains (A and B) are specifically linked together by disulfide linkages.
- Disulfide linkages are covalent bonds formed between the sulfur atoms of cysteine residues in the polypeptide chains.

5. **Conclusion**:
- Therefore, the correct answer to the question is that the two polypeptide chains of insulin are held together by disulfide linkages.

### Final Answer:
The two polypeptide chains of insulin are held together by **disulfide linkages**.

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