The simplest of the amino acids is glycine, a non-essential building block with a single hydrogen as its side chain. Collagen is rich in it, with glycine residues repeating through the triple helix alongside high levels of proline, alanine and valine. Food makers use it as a sweet-tasting flavour enhancer and as a buffering agent, and it carries the E number E640 with its salts. Its small size lets it fit where bulkier amino acids cannot, which matters in protein structure.