Functional workhorses of the cell
Polymers of amino acids
Proteins are polymers of amino acids linked by peptide bonds. Their sequence — the primary structure — drives folding into alpha-helices and beta-sheets (secondary structure), and ultimately into a precise three-dimensional shape (tertiary structure) that determines function. Proteins serve as enzymes, structural scaffolds, signal receptors, transporters, and much more. A single human cell contains tens of thousands of distinct proteins.