In biochemistry, what best describes the tertiary structure of a protein?

• A. The arrangement and interaction of multiple polypeptide subunits to form a functional protein complex
• B. The linear sequence of amino acids in a polypeptide chain linked by peptide bonds
• C. Local folding patterns such as $\alpha$-helices and $\beta$-sheets stabilized primarily by backbone hydrogen bonding
• D. The overall three-dimensional folding of a single polypeptide chain formed by interactions among side chains (R groups), including hydrophobic interactions, hydrogen bonds, ionic interactions, and disulfide bonds

Answer: (D)