Figure 4-29. Aminoacylation of tRNA. Amino acids are covalently linked to tRNAs by aminoacyl-tRNA synthetases.

Figure 4-29Aminoacylation of tRNA. Amino acids are covalently linked to tRNAs by aminoacyl-tRNA synthetases

Each of these enzymes recognizes one kind of amino acid and all the cognate tRNAs that recognize codons for that amino acid. The two-step aminoacylation reaction requires energy from the hydrolysis of ATP. The equilibrium of the overall reaction favors the indicated products because the pyrophosphate (PPi) released in step 1 is converted to inorganic phosphate (Pi) by a pyrophosphatase. The 3′ end of all tRNAs, to which the amino acid attaches, has the sequence CCA. Class I synthetases (purple) attach the amino acid to the 2′ hydroxyl of the terminal adenylate in tRNA; class II synthetases (green) attach the amino acid to the 3′ hydroxyl. (Ad = adenine; Cyt = cytosine.)

From: Section 4.4, The Three Roles of RNA in Protein Synthesis

Cover of Molecular Cell Biology
Molecular Cell Biology. 4th edition.
Lodish H, Berk A, Zipursky SL, et al.
New York: W. H. Freeman; 2000.
Copyright © 2000, W. H. Freeman and Company.

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