Proteinogenic amino acids are those 22 amino acids that're found in proteins and that're coded for in the standard genetic code. Proteinogenic literally means protein building. Proteinogenic amino acids are assembled into a polypeptide (the subunit of a protein) through a process known as translation (the second stage of protein biosynthesis, part of the overall process of gene expression). Non-proteinogenic amino acids are either not found in proteins (like carnitine, GABA, or L-DOPA), or not c… (More on Nonproteinogenic)