Final answer:
Cysteine is the amino acid that forms disulfide bonds, which are crucial for protein structure and stability.
Step-by-step explanation:
The amino acid involved in the formation of disulfide bonds is cysteine. Cysteine contains a sulfhydryl (SH) group in its side chain, which can be oxidized to form a disulfide (S-S bond) when two cysteine molecules come into proximity within a protein. The disulfide bond is covalent and greatly stabilizes the protein's structure by linking different parts of the protein chain or different protein chains together. This covalent bond is critical for the folding and stability of proteins such as insulin.