There are 20 known standard amino acids, which are well known as components of protein (proteinogenic), but some are also important as neurotransmitters or intermediary for synthesis of other molecules. The sequence of amino acids in a protein are related to the function of that protein and are determined by the genetic code in the DNA. Over 100 amino acids are found in nature.

Amino acids are molecules that contain a basic amino (NH2) group, an acidic carboxyl (COOH) group and a side chain (R for carbon chain) attached to an alpha carbon atom.

All amino acids have the L configuration (Wikipedia: optical isomerism), except for glycine, which is optically neutral.

Amino acids form linear arrays to form proteins.

Essential amino acids are amino acids that cannot be synthesized by the body (varies from species to species). The essential amino acids are:

Phenylalanine, Valine, Tryptophan

Threonine, Isoleucine, Methionine

Histidine, Arginine, Lysine, Leucine

Note: Mnemonic device for remembering these is “Private Tim Hall”, abbreviated as: PVT TIM HALL

Branch chain amino acids are:
leucine, isoleucine and valine

Non-standard amino acids are biologically-important: GABA (neurotransmitter), carnitine (used in lipid transport within a cell), ornithine, citrulline, homocysteine, hydroxyproline, hydroxylysine, and sarcosine.

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