What organic monomer serves as the building block of proteins?

• A. Carbohydrate
• B. Amino Acid
• C. Nucleic Acid
• D. Fatty Acid

Answer: (B)

Proteins are built from amino acids, the monomers that join together to form polypeptides. Each amino acid has an amino group and a carboxyl group; when two amino acids link, a peptide bond forms in a condensation reaction, releasing a molecule of water. Repeating this process creates a long chain—the primary structure of a protein—which folds into its three-dimensional form and governs function. There are 20 standard amino acids with different side chains that give proteins their diverse properties and activities.

Carbohydrates are built from sugar units (monosaccharides), nucleic acids from nucleotides, and lipids from fatty acids (often with glycerol). These other biomolecule families use different monomers, not amino acids, as their building blocks.