Amino acids. Computer-generated molecular models of 5 amino acids. Clockwise from top left: glycine (C2H5NO2), alanine (C3H7NO2), valine (C5H11NO2), isoleucine (C6H13N02), leucine (C6H13NO2). The colored spheres represent different atoms: oxygen (light blue), carbon (red), hydrogen (white), nitrogen- (dark blue). Amino acids are the building blocks of proteins, which control the biochemical activity inside all living cells. There are 20 different types of amino acids but millions of different proteins. Genes specify exactly how the different amino acids are put together to make a protein, and this determines the protein's shape, which in turn determines its function.