Disulfide bridges are formed when the side chains of two amino acid residues react - VCE - SSCE Chemistry - Question 16 - 2010 - Paper 1

To determine which pair of amino acids can form disulfide bridges, we need to consider the properties of the amino acids involved. Disulfide bridges are formed specifically by the oxidation of two cysteine residues, which contain thiol (-SH) groups in their side chains.

1. Cysteine and Serine (Option A): While serine has an alcohol group (-OH) in its side chain, it does not have the capacity to form disulfide bridges with cysteine.

2. Cysteine and Glycine (Option B): Glycine, being the simplest amino acid, cannot contribute to the formation of disulfide bridges as it lacks a reactive side chain.

3. Cysteine and Cysteine (Option C): This is the correct option since two cysteine residues have thiol groups that can oxidize to form a disulfide bond (–S–S–).

4. Cysteine and Glutamic Acid (Option D): Glutamic acid contains a carboxyl (-COOH) group, which cannot participate in disulfide bond formation with cysteine.

In conclusion, the only suitable pair for forming disulfide bridges is cysteine and cysteine. Thus, the correct answer is: C. cysteine and cysteine.