Amino Acids

Proteins are defined by their unique sequence of amino acid residues. Twenty-two standard amino acids are used by cells in protein biosynthesis, and these are specified by the general genetic code. These twenty-two amino acids are biosynthesized from other molecules, but organisms differ in which ones they can synthesize and which ones must be provided in their diet. The ones that cannot be synthesized by an organism are called essential amino acids.
Essential - Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, Valine.
However, not all of the functions of other abundant non-standard amino acids are known, for example taurine is a major amino acid in muscle and brain tissues, but although many functions have been proposed, its precise role in the body has not been determined.