Aminoacyl-tRNA binding

Translation Elongation Charged aminoacyl-tRNA binds to A site (GTP) Charged aminoacyl-tRNA binds to A site (GTP)... 

The elongation reactions begin with the binding of the aminoacyl-tRNA specified by the codon immediately adjacent to the initiator codon. The binding of this aminoacyl-tRNA is catalyzed by an aminoacyl-tRNA binding factor,... 

The final step in elongation is known as translocation (fig. 29.17). This reaction, like aminoacyl-tRNA binding, is catalyzed by a factor (the translocation factor, known as EF-G in prokaryotic systems and EF-2 in eukaryotic systems) that cycles on and off the ribosome and hydrolyzes GTP in the process. The overall purpose of translocation is to move the ribosome physically along the mRNA to expose the next codon for translation. 

At the start of the first round of elongation (Fig. 5), the initiation codon (AUG) is positioned in the P site with fMet-tRNAfMet bound to it via codon-anticodon base-pairing. The next codon in the mRNA is positioned in the A site. Elongation of the polypeptide chain occurs in three steps called the elongation cycle, namely aminoacyl-tRNA binding, peptide bond formation and translocation ... 

After translocation, the A site is empty and ready to receive the next aminoacyl-tRNA. The A site and the E site cannot be occupied simultaneously. Thus the deacylated tRNA is released from the E site before the next aminoacyl-tRNA binds to the A site to start a new round of elongation. Elongation continues, adding one amino acid to the C-terminal end of the growing polypeptide for each codon that is read, with the peptidyl-tRNA moving back and forth from the P site to the A site as it grows. 

PS (inhibits aminoacyl tRNA binding to ribosome) [antibacterial]... 

Several sites on the ribosome interact with tRNA (Fig. 4.1) and also are targeted by antibiotics. The peptidyl-tRNA binding site (P-site) of the large subunit binds to the 3 end of peptidyl-tRNA. The aminoacyl-tRNA binding site (A-site) of the... 

Chloramphenicol inhibits protein synthesis by binding to the 50S subunit of the bacterial ribosome and blocking aminoacyl-tRNA binding. 

Figure 29.24. Mechanism of Protein Synthesis. The cycle begins with peptidyl-tRNA in the P site. An aminoacyl-tRNA binds in the A site. With both sites occupied, a new peptide bond is formed. The tRNAs and the mRNA are translocated through the action of elongation factor G, which moves the deacylated tRNA to the E site. Once there, it is free to dissociate to complete the cycle.

The ribosome includes three sites for tRNA binding called the A (aminoacyl) site, the P (peptidyl) site, and the E (exit) site. With a tRNA attached to the growing peptide chain in the P site, an aminoacyl-tRNA binds to the A site. A peptide bond is formed when the amino group of the aminoacyl-tRNA nucleophically attacks the ester carbonyl group of the peptidyl-tRNA. On peptide-bond formation, the tRNAs and mRNA must be translocated for the next cycle to begin. The deacylated tRNA moves to the E site and then leaves the ribosome, and the peptidyl-tRNA moves from the A site into the P site. 

Grp, Group antibiotic group specificity A, inhibitors of aminoacyl—tRNA binding B, inhibitors of peptide bond formation C, inhibitors of translocation. 

Chlortetracyclin inhibits protein synthesis by binding to the 30S subunit of ribosomes and prevents the aminoacyl-tRNA binding to the A site on the ribosome. This prevents the codon-anticodon interaction from taking place. Protein release is also inhibited. 

Tetracycline Binding to 30S subunit interferes with aminoacyl-tRNA binding... 

EF-Tu will bind to any aminoacylated tRNA other than tRNA the initiator tRNA (step c. Fig. 29-12), and carry it to the ribosome (step d), where it binds into the A site. There it is selected if it forms a proper base pair with the mRNA codon in the A site or is rejected if it does not. This decoding process involves both an initial step and a proofreading step. The aminoacyl-tRNA binds both to the decoding site in the 16S RNA and to the peptidyltransferase site in the 23S RNA. (See discussions on p. 1687.) The decoding site is on the platform at the upper end of helix 44 (Fig. 29-2). Nucleotide G1401 plays a crucial roie.375 vVhen one of the isoacceptor species of E. coU tRNA is irradiated with ultraviolet light, the... 

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