What are proteins primarily made of?

Proteins are primarily made of amino acids, which are organic compounds composed of carbon, hydrogen, oxygen, and nitrogen. Amino acids serve as the building blocks of proteins, and they link together through peptide bonds to form polypeptides. Each protein's unique sequence of amino acids determines its structure and function in the body.

Unlike fatty acids, which are components of lipids, and starch molecules, which are carbohydrates used for energy storage, amino acids specifically play a critical role in the formation of proteins. Nucleotides, on the other hand, are the building blocks of nucleic acids like DNA and RNA, rather than proteins. Thus, the correct answer highlights the fundamental role amino acids play in protein synthesis and the biological significance of proteins in various physiological processes.