Which biomolecule is a three-dimensional polymer made of amino acids?

• A. Protein
• B. Carbohydrate
• C. Nucleic acid
• D. Lipid

Answer: (A)

Proteins are polymers built from amino acids linked by peptide bonds, and they fold into a specific three-dimensional shape. The sequence of amino acids—primary structure—drives how the chain folds into secondary structures like helices and sheets, which then fold further into the final tertiary (and sometimes quaternary) structure. That 3D arrangement is essential because it creates the active sites of enzymes, binding pockets, and structural features that determine function. Carbohydrates are polymers of sugar units, nucleic acids are polymers of nucleotides, and lipids are not formed as repeating amino-acid polymers, so they don’t match the description of a three-dimensional polymer made from amino acids.