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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.

7.

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“ “ .