Final answer:
Proteins are macromolecules composed of amino acid monomers, these polymers of amino acids play crucial roles in cellular structure and metabolic reactions. So the correct option is C.
Step-by-step explanation:
The macromolecule that is comprised of amino acid monomers is proteins. Amino acids are organic compounds with a basic amino group (NH2) and an acidic carboxyl group (COOH), as well as a hydrogen atom and a variable side chain or R-group. These amino acids link together through peptide bonds in a dehydration reaction to form polymers known as proteins, which are essential to many functions in living organisms. Among the biological macromolecules, proteins uniquely serve as the building blocks of cellular structure and the acting catalysts in metabolic reactions.