Understand the definition of a monomer: A monomer is a small molecule that can bind chemically to other molecules to form a polymer.
Identify the polymer in question: Proteins are polymers made up of monomers.
Recall the structure of proteins: Proteins are composed of long chains of amino acids linked by peptide bonds.
Match the monomer to the polymer: Amino acids are the building blocks or monomers of proteins.
Review the other options: Monosaccharides are monomers of carbohydrates, fatty acids are components of lipids, and nucleotides are monomers of nucleic acids.