Aminoacyl tRNA synthases

Synthases Attach Amino Acids to tRNAs Each Synthase Recognizes a Specific Amino Acid and Specific Regions on Its Cognate tRNA Aminoacyl-tRNA Synthases Can Correct Acylation Errors... 

A unique class of enzymes, called aminoacyl-tRNA synthases, attach amino acids to their cognate tRNAs. This attachment serves two functions (1) The linkage between... 

The second reaction catalyzed by the aminoacyl-tRNA synthases results in the attachment of the amino acid through an ester linkage to the 3 terminal ribose of tRNA ... 

Aminoacyl-tRNA Synthases Can Correct Acylation Errors... 

Many aminoacyl-tRNA synthases appear to contain a second catalytic site that serves to correct errors by hydrolyzing incorrectly matched amino acids and tRNAs. These proof-reading hydrolysis reactions are best understood in the case... 

Identity elements in four tRNAs. Each circle represents one nucleotide. Filled circles indicate nucleotides that serve as recognition elements to the appropriate aminoacyl-tRNA synthase. It is possible that other identity elements occur in these structures that are still to be discovered. (From L. H. Schulman and J. Abelson, Recent excitement in understanding transfer RNA identity, Science 240 1591, June 17, 1988. Copyright 1988 by the AAAS. Reprinted by permission.)... 

All tRNA s are similar in structure (Fig. 12.5). The TDC arm participates in binding of the charged tRNA to a site on the ribosome where protein synthesis occurs. The DHU (or D) arm is necessary for recognition by the proper aminoacyl tRNA synthase (the enzyme). The acceptor end is at the 3 terminus and ends in the sequence CAA. The anticodon arm consists of seven nucleotides, the sequence of which is read 3 to 5 (opposite convention to the usual 5 to 3 ). The anticodon sequence is 3 variable base modified purine-X-Y-Z-Py-Py 5. The central bases, X, Y, Z comprise the anticodon, codon 5 ... 

The amino is linked via the 5 position to the ribose on the ATP, liberating PPi. Notice the amino-AMP complex remains bound to the enzyme, aminoacyl tRNA synthase. 

Concerning the activation of amino acids for constructing the peptide bond, the folloiving process has been elucidated (Fig. 3). The first step is the formation of adenosine monophosphate of an amino acid (aminoacyl-AMP) by the reaction of an amino acid and adenosine triphosphate (ATP) catalyz by aminoacyl-tRNA synthase (ARS). The resulting aminoacyl-AMP is further attacked by a hydroxyl group of a specific transfer RNA giving rise to an aminoacyl-tRNA as a precursor for the peptide bond formation. 

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