Amino Acids and Disulfide Bond Formation

Amino acids are the building blocks of proteins and play a crucial role in various biological processes. Each amino acid has a unique side chain (R group) that determines its properties and function. Understanding the biochemical properties of amino acids is essential for grasping how proteins fold and function.

Among the 20 standard amino acids, which of the following amino acids contains a sulfur atom in its side chain and can form disulfide bonds important for stabilizing protein structures?