Genetics: Analysis and Principles 5th Edition by Robert Brooker

Exercise 27

According to Figure 13.17, explain why the ribosome translocates along the mRNA in a 5 to 3 direction rather than a 3 to 5 direction.FIGURE 13.17 The elongation stage of translation in bacteria. This process begins with the binding of an incoming charged tRNA. The hydrolysis of GTP by EF-Tu provides the energy for the binding of the tRNA to the A site. A peptide bond is then formed between the amino acid at the A site and the last amino acid in the growing polypeptide. This moves the polypeptide to the A site. The ribosome then translocates in the 3. direction so the two tRNAs are moved to the E and P sites. The tRNA carrying the polypeptide is now back in the P site. This translocation requires the hydrolysis of GTP via EF-G. The uncharged tRNA in the E site is released from the ribosome. Now the process is ready to begin again. Each cycle of elongation causes the polypeptide to grow by one amino acid.