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Amino Acids

All peptides and proteins are polymers of alpha-amino acids. An amino acid is a molecule that contains both amino (NH2) and carboxyl (COOH) functional groups. Alanine is one of the standard amino acids:

Twenty standard amino acids are used by cells in peptide biosynthesis, and these are specified by the general genetic code. Amino acids are classified into two groups: essential amino acids and nonessential amino acids.

An essential amino acid or indispensable amino acid cannot be made by the body and must be supplied by food. These include isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Another amino acid - histidine is considered semi-essential because the body does not always require dietary sources of it.

Nonessential amino acids are made by the body from the essential amino acids or normal breakdown of proteins. The nonessential amino acids are arginine, alanine, asparagine, aspartic acid, cysteine, glutamine, glutamic acid, glycine, proline, serine, and tyrosine.

The classification of an amino acid as essential or nonessential does not reflect its importance, because all 20 amino acids are necessary for health.

IUPAC recommendations on Amino Acid and Peptide Nomenclature is available for download in Adobe Acrobat format.