Medically reviewed by Aviv Joshua, MS, RDN Phenylalanine is an essential amino acid (building block of protein) that the body ...

The present work was carried out, using phenylalanine labelled with carbon-14, to examine whether phenylalanine is a precursor of tyrosine.

During that same year, Marshall Nirenberg and Heinrich Matthaei began deciphering the genetic code, and they determined that the codon UUU specifically represented the amino acid phenylalanine.