chapter 25
RNA and Protein Synthesis
FIGURE 25-12
Elongation phase of protein synthesis: binding of charged tRNA, peptide bond formation, and translocation. Note that
this phase consumes 2 GTP during each cycle of chain elongation.
accomplished by release factors (RFs), which are
proteins that, in part, respond to chain termination
codons. In the presence of release factors,
peptidyltransferase catalyzes the reaction of the
bound peptidyl moiety with water rather than with the
free aminoacyl tRNA (Figure 25-14). Thus, the
polypeptide chain, which has been held in the
ribosome solely by the interaction with the tRNA in
the P site, is released from the ribosome.
Dissociation of the 70S ribosome.
The 70S ribosome
dissociates into 30S and 50S subunits, which may
start synthesis of another polypeptide chain.
FIGURE 25-13
Peptide bond formation in prokaryotes. In eukaryotes, the chemistry is the same, although the initiating tRNA is not
tRNAfMet but tRNA“ “ .
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