An antibody contains light and heavy chains interconnected by disulphide bonds. These disulphide bonds can be formed between

Options

A. serine, theonine
B. methionine, cysteine
C. methionine, methionine
D. cysteine, cysteine

Answer

To solve the question regarding the formation of disulfide bonds in antibodies, we need to analyze the options provided and understand the chemistry behind disulfide bond formation.

### Step-by-Step Solution:

1. **Understanding Disulfide Bonds**: Disulfide bonds are covalent bonds that can form between the sulfur atoms of two cysteine residues. This bond is crucial for the stability and structure of proteins, including antibodies.

2. **Analyzing the Options**:
- **Option A: Serine and Threonine** - These amino acids do not contain sulfur in their side chains, so they cannot form disulfide bonds.
- **Option B: Methionine and Cysteine** - Methionine contains sulfur, but it does not form disulfide bonds like cysteine does. Methionine has a thioether group, which does not participate in disulfide bond formation.
- **Option C: Methionine and Methionine** - Again, since methionine does not form disulfide bonds, this option is incorrect.
- **Option D: Cysteine and Cysteine** - This option is correct because cysteine contains a thiol (-SH) group that can oxidize to form a disulfide bond (–S–S–) with another cysteine.

3. **Conclusion**: The correct answer is **D: Cysteine and Cysteine**. Disulfide bonds in antibodies are formed specifically between cysteine residues.