<prompt> Essential amino acid is:PhenylalanineProlineGlutamineSerine  <response>: Phenylalanine It is an alpha-amino acid. This essential amino acid is classified as nonpolar because of the hydrophobic nature of the benzyl side chain. L-Phenylalanine LPA is an electrically neutral amino acid The codons for L-phenylalanine are UUU and UUC. Phenylalanine is a precursor for tyrosine, the monoamine signaling molecules dopamine, norepinephrine noradrenaline, and epinephrine adrenaline, and the skin pigment melanin. 