Reaction Ribosome shift

The positive charge on 2451A in the tetrahedral intermediate is probably transferred to adjacent tRNA nucleotides that undergo tautomeric shifts. The evidence that ribosomal RNAs perform enzymatic functions critical to protein synthesis lends weight to the evolutionary significance of RNA in primordial chemical reactions that eventually led to the development of cells. 

In detail, the 3 -hydroxy-group of the ribose (in the terminal adenosine residue of each tRNA molecule) is acylated, enzymatically, by an activated form of that amino acid for which this tRNA is specific. Amide-ester exchange of these esters with peptidyl-tRNA on the ribosomes then occurs under the direction of mRNAs. In the latter step, the growing peptide is transferred from the tRNA bond on the donor site of the ribosomes to an aminoacyl-tRNA bond on the acceptor site of the same ribosome. This reaction is catalysed by the enzyme peptidyl transferase. The peptide, lengthened in this way, is then entirely shifted to the donor site with the help of a translocation enzyme. The next aminoacyl-tRNA then becomes bound to the vacant acceptor site, and the process is repeated. The terminal groups of the tRNAs are always —XCCA, where C is a cytidylic, and A an adenylic, acid residue. 

Finally, a photoinduced reaction of unmodified chloramphenicol with the ribosome has been observed. The reaction is expressed in the labeling of several ribosomal proteins and in a pronounced shift in the electrophoretic mobility of protein L19. "... 

The role of GTP in EF-Tu-promoted binding of aminoacyl-tRNA could be formulated as follows. First, a unique conformation of EF-Tu induced by GTP can select exclusively the aminoacylated form of tRNA in preference to its deacylated form. Second, the ternary complex, aminoacyl-tRNA-EF-Tu-GTP, is transferred to a precise location on the 508 ribosomal subunit through the conformation of EF-Tu-GTP favorable for interaction with ribosomes. The conformational change of aminoacyl-tRNA induced by complexing with EF-Tu-GTP may also serve for this interaction. Third, after the transfer of aminoacyl-tRNA to the A site of ribosomes, EF-Tu is to be released from ribosomes to reinitiate a new cycle of reactions. This could be accomplished by the hydrolysis of bound GTP to GDP. An additional advantage of the split of GTP is to shift the equilibrium irreversibly... 

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