Amino acids are used by cells to build proteins. All amino acids share a common “connector”, making it possible for a single ribosome enzyme to assemble hundreds of amino acids together into a long strand. This connector consists of an amine and a carboxylic acid group. Here, the standard connector is shown in red as a phenylalanine amino acid chemically bonds with a glutamine amino acid, releasing a water molecule in the process. A different enzyme can be used to take a strand of amino acids apart.

Depending on the chemical structure of the rest of the molecule, amino acids can be polar or nonpolar, and have different geometries, sizes, and chemical properties. The sequence of amino acids in a protein determines how a protein will fold and the binding sites it will have.