Proteinogenic amino acids are amino acids that are precursors to proteins, and are incorporated into proteins during translation. Throughout known life, there are 23 proteinogenic amino acids, 20 in the standard genetic code and an additional 3 that can be incorporated by special translation mechanisms. The word "proteinogenic" means "protein creating". Proteinogenic amino acids can be condensed into a polypeptide (the subunit of a protein) through a process called translation (the second stage of protein biosynthesis, part of the overall process of gene expression).