If we observe the structure of proteins, disulphide bonds are formed between

Options

A. Cysteine residues that are close together
B. Cystine residues that are close together
C. Proline residues that are close together
D. Histidine residues that are close together

Answer

To solve the question regarding the formation of disulfide bonds in proteins, follow these steps:

### Step-by-Step Solution:

1. **Identify the Components of Proteins**:
- Proteins are made up of amino acids, which consist of an amino group, a carboxyl group, a hydrogen atom, and a variable R group.

2. **Understand the Role of Cysteine**:
- Among the amino acids, cysteine is unique because it contains a thiol (-SH) group in its side chain (R group). This is important for the formation of disulfide bonds.

3. **Formation of Disulfide Bonds**:
- When two cysteine residues come close together, their thiol groups can undergo oxidation. This reaction leads to the formation of a covalent bond known as a disulfide bond (–S–S–).

4. **Identify the Correct Answer**:
- The question asks between which residues disulfide bonds are formed. The correct answer is:
- **A) Cysteine residues that are close together**.
- This is because disulfide bonds specifically form between the thiol groups of cysteine residues.

### Final Answer:
Disulfide bonds are formed between **cysteine residues that are close together** (Option A).

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