Translations:Amino acid/72/en

Many proteinogenic and non-proteinogenic amino acids have biological functions beyond being precursors to proteins and peptides.In humans, amino acids also have important roles in diverse biosynthetic pathways. Defenses against herbivores in plants sometimes employ amino acids. Examples:

Standard amino acids

• Tryptophan is a precursor of the neurotransmitter serotonin.
• Tyrosine (and its precursor phenylalanine) are precursors of the catecholamine neurotransmitters dopamine, epinephrine and norepinephrine and various trace amines.
• Phenylalanine is a precursor of phenethylamine and tyrosine in humans. In plants, it is a precursor of various phenylpropanoids, which are important in plant metabolism.
• Glycine is a precursor of porphyrins such as heme.
• Arginine is a precursor of nitric oxide.
• Ornithine and S-adenosylmethionine are precursors of polyamines.
• Aspartate, glycine, and glutamine are precursors of nucleotides. However, not all of the functions of other abundant nonstandard amino acids are known.