The two polypeptides of human insulin are linked together by

Options

A. Hydrogen bonds
B. Phosphodiester bond
C. Covalent bond
D. Disulphide bridges

Answer

To solve the question about how the two polypeptides of human insulin are linked together, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Polypeptides**:
- A polypeptide is a chain of amino acids linked together by peptide bonds. In the case of insulin, it consists of two chains known as chain A and chain B.

2. **Identifying the Types of Bonds**:
- We need to evaluate the types of bonds mentioned in the options: hydrogen bonds, phosphodiester bonds, covalent bonds, and disulfide bridges.

3. **Evaluating Each Option**:
- **Hydrogen Bonds**: These are weak interactions and are not primarily responsible for linking the polypeptides in insulin.
- **Phosphodiester Bonds**: These bonds are found in nucleic acids (like DNA and RNA) and do not apply to proteins like insulin.
- **Covalent Bonds**: While covalent bonds are strong, they do not specifically describe the linkage between the two polypeptides in insulin.
- **Disulfide Bridges**: These are a specific type of covalent bond formed between the sulfur atoms of cysteine residues in proteins. They play a crucial role in stabilizing the structure of proteins.

4. **Conclusion**:
- The two polypeptides of human insulin (chain A and chain B) are linked together by disulfide bridges. This type of bond is essential for maintaining the functional structure of insulin.

### Final Answer:
The two polypeptides of human insulin are linked together by **disulfide bridges**.

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