Final answer:
Proteins are made of amino acids containing nitrogen, bonded by peptide bonds, and each has a unique R group alongside an amino and a carboxyl group.
Step-by-step explanation:
Proteins contain carbon, hydrogen, oxygen, and nitrogen, reflecting their role as organic compounds with vital functions in cells. Proteins are comprised of chains of amino acids held together by peptide bonds. Each amino acid contains an amino group (-NH₂), a(n) carboxyl group (-COOH), and a unique side chain, known as the R group, which determines the specific properties of each amino acid.