Chain: polar
Codons: TAC TAT
Tyrosine (codons: TAC, TAT) 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 a side chain containing an aromatic phenyl group bonded to a hydroxy group, making it a polar 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−).
Tyrosine is one of the 20 amino acids encoded in the standard genetic code and is conditionally non-essential in humans, since it can be synthesized from the essential amino acid phenylalanine. In other organisms, such as plants and microorganisms, it is synthesized through the shikimate pathway. Tyrosine is a precursor to numerous biologically important substances, such as DOPA, dopamine, catecholamines (e.g. norepinephrine and epinephrine), melanin, thyroxine and tyramine. Similar to other amino acids which side chain contains a hydroxyl group, tyrosine can be phosphorylated, besides other posttranslational modifications, and therefore plays a role in activation and inactivation of enzymes.
In 1846, tyrosine was first isolated from casein protein of cheese by Justus von Liebig, who named in reference to the Greek word for cheese ("tyros").
Properties
Side chain: hydrophilic (polar, uncharged)
Chemical formula: C₉H₁₁NO₃
Molar mass: 181.19 g/mol
Density: 1.46 g/cm³