Tryptophan (Trp or W) is an α-aminoacid used in biosynthesis of proteins. It contains an α-amino group, an α-carboxylic acid group and a side chain indole, making it a polar molecule with non-polar aromatic beta carbon substituent. Trp is a precursor for serotonin, melatonin and vitamin B3. It is encoded by the codon UGG.