phenylalanine

noun

Etymology: From phenyl + alanine.

1. An essential amino acid C₉H₁₁NO₂ found in most animal proteins; it is essential for growth; the inability to metabolize it leads to phenylketonuria; it is a constituent of aspartame.

   “Nash Hensley, of South Bend, Indiana, was born with two genetic disorders: achondroplasia, a bone growth disorder characterized by dwarfism, and phenylketonuria, or PKU, which causes the phenylalanine amino acid to build up in the body, according to the Mayo Clinic. PKU is caused by a defect in the gene that produces the enzyme needed to break down phenylalanine, so Nash is required to live on a restricted, low-protein diet.”

2. This molecule or its D-isomer.