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Phenylalanine
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<p>Phenylalanine (symbol Phe or F) is an essential α-<a href="/facts/Amino_acid/WDxYwBny">amino acid</a> with the <a href="/facts/Chemical_formula/hghUtthl">formula</a> C9H11NO2. It can be viewed as a <a href="/facts/Benzyl/kHmqYwqH">benzyl</a> group <a href="/facts/Substituent/6y9IE6G0">substituted</a> for the <a href="/facts/Methyl_group/fkM97EMD">methyl group</a> of <a href="/facts/Alanine/fphQEdSc">alanine</a>, or a <a href="/facts/Phenyl/Ql9Yx5uu">phenyl</a> group in place of a terminal hydrogen of alanine. This <a href="/facts/Essential_amino_acid/Re9Rxb9I">essential amino acid</a> is classified as neutral, and <a href="/facts/Chemical_polarity/KlIJ0zjB">nonpolar</a> because of the inert and <a href="/facts/Hydrophobic/Ifya0CXQ">hydrophobic</a> nature of the <a href="/facts/Benzyl/kHmqYwqH">benzyl</a> side chain. The <a href="/facts/Chirality_(chemistry)/p5a9pftB">L-isomer</a> is used to biochemically form <a href="/facts/Protein/Jxmagu3E">proteins</a> coded for by <a href="/facts/DNA/nB89Iauz">DNA</a>. Phenylalanine is a precursor for <a href="/facts/Tyrosine/RJhEgE4C">tyrosine</a>, the <a href="/facts/Monoamine_neurotransmitter/TduN5yes">monoamine neurotransmitters</a> <a href="/facts/Dopamine/5gNy8Xkd">dopamine</a>, <a href="/facts/Norepinephrine/AjTIC9ox">norepinephrine</a> (noradrenaline), and <a href="/facts/Epinephrine/k7vvMI7E">epinephrine</a> (adrenaline), and the <a href="/facts/Biological_pigment/7Lv9jMEd">biological pigment</a> <a href="/facts/Melanin/QtGsXAm4">melanin</a>. It is <a href="/facts/Genetic_code/zUK0bY1B">encoded</a> by the <a href="/facts/Messenger_RNA/oUL6qxQn">messenger RNA</a> <a href="/facts/Codons/zUK0bY1B">codons</a> UUU and UUC. </p><p>Phenylalanine is found naturally in the milk of <a href="/facts/Mammal/phSwTzBo">mammals</a>. It is used in the manufacture of food and drink products and sold as a nutritional supplement as it is a direct precursor to the <a href="/facts/Neuromodulation/mwjkrkHt">neuromodulator</a> <a href="/facts/Phenethylamine/XyjysSul">phenethylamine</a>. As an essential amino acid, phenylalanine is not synthesized <a href="/facts/De_novo_synthesis/mDEr4L0K">de novo</a> in humans and other animals, who must ingest phenylalanine or phenylalanine-containing proteins. </p><p>The one-letter symbol F was assigned to phenylalanine for its phonetic similarity. </p>