Chain: nonpolar
Codons: TGG
Tryptophan (codon: TGG) is an α-amino acid that is used in the biosynthesis of proteins, specifically its L-isomer (left-handed). It contains an α-amino group, an α-carboxylic acid group, and an aromatic indole side chain, making it a nonpolar amino acid. At physiological pH (7.4), the amino group is in the protonated form (−NH₃⁺) and the carboxyl group is in the deprotonated form (−COO−).
Tryptophan is one of the 20 amino acids encoded in the standard genetic code and is essential in humans, meaning that it cannot be metabollically synthesized, and must be obtained from the diet. In other organisms, such as plants and microorganisms, it is synthesized through the shikimate pathway. Tryptophan is a precursor to the neurotransmitter serotonin and the hormone melatonin, and other biologically important substances. While tryptophan is less abundant in proteins, it plays important structural and functional roles, for example in the attachment of membrane proteins to cell membranes.
In 1901, tryptophan was first isolated from the casein protein of milk by Frederick Hopkins. He later demonstrated that it is essential for animals.
Properties
Side chain: hydrophobic (nonpolar, uncharged)
Chemical formula: C₁₁H₁₂N₂O₂
Molar mass: 204.23 g/mol
Density: 1.40 g/cm³