Tyrosine (Y)

Tyrosine (Tyr or Y) or 4-hydroxyphenylalanine is one of the 20 standard amino acids that are used by cells to synthesize proteins. It is a non-essential amino acid with a polar side group. Its codons are UAC and UAU. The word "tyrosine" is from the Greek tyros, meaning cheese, as it was first discovered in 1846 by German chemist Justus von Liebig in the protein casein from cheese. It is called tyrosyl when referred to as a functional group or side chain. Tyrosine is a hydrophilic amino acid and is significantly more soluble in water than its precursor, phenylalanine, due to the thermodynamic favorability of the hydrogen bonding between the hydroxyl group of one molecule of tyrosine and the carboxyl group of another.