FIGURE 5-19 Translating nucleic acid sequence into amino acid sequence. (a) The process for translating nucleic acid sequences in mRNA into amino acid sequences in proteins involves two steps. Step 1: An aminoacyl-tRNA synthetase first couples a specific amino acid, via a high-energy ester bond (yellow), to either the 2′ or 3′ hydroxyl of the terminal adenosine in the corresponding tRNA. Step 2: A three-base sequence in the tRNA (the anticodon) then base-pairs with a codon in the mRNA specifying the attached amino acid. If an error occurs in either step, the wrong amino acid may be incorporated into a polypeptide chain. Phe = phenylalanine. (Note that this is a simplified diagram of tRNA^Phe; its actual structure is shown in Figure 5-20b.) (b) Molecular model of the human mitochondrial aminoacyl-tRNA synthetase for Phe in complex with tRNA^Phe.

[Data from Klipcan L., et al., 2012. J. Mol. Biol. 415:527, PDB ID 3tup.]