Final answer:
Proteins are composed of amino acids, which are linked together by peptide bonds to form polypeptide chains.
Step-by-step explanation:
Proteins are composed of amino acids. Amino acids are organic compounds that contain an amino group (-NH2) and a carboxyl group (-COOH). They are the building blocks of proteins and are linked together by peptide bonds to form polypeptide chains. Each amino acid has a unique side chain or R group, which determines its chemical properties and role in protein structure and function.
Learn more about Composition of proteins