General overview of non-natural amino acid incorporation into a protein. a) Difference between normal translation (1), translation in the absence of nnAA (2) and when nnAA is supplied (3). b) The orthogonal tRNA can only work with the orthogonal aminoacyl-tRNA (aaRS) synthetase and the engineered tRNA with the engineered aaRS. In the presence of the UAG codon and supplied nnAA the end result is a modified peptide molecule with the non-natural incorporated.