At the elemental level, proteins contain carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sulfur (S). Some proteins also contain phosphorus (P), iron (Fe), copper (Cu), and other elements in trace amounts. These elements are arranged in a specific sequence of amino acids, which are linked together by peptide bonds to form a polypeptide chain. The structure of a protein determines its function, and proteins play a crucial role in numerous biological processes, including metabolism, enzyme catalysis, hormone regulation, and immune response.