Proteins are composed of what smaller subunits?

• A. Nucleotides
• B. Amino acids
• C. Monosaccharides
• D. Fatty acids

Answer: (B)

Proteins are built from amino acids, the small blocks that link together to form long chains called polypeptides. Each amino acid has an amino group and a carboxyl group, and they join through peptide bonds in a dehydration synthesis reaction. The order of amino acids in a chain determines how it folds into a specific shape, which in turn dictates the protein’s function in the cell. Other molecules use different building blocks—nucleotides for nucleic acids, monosaccharides for carbohydrates, and fatty acids for lipids—so they aren’t the subunits of proteins. Amino acids are the basic subunits that compose proteins.