by PhilipJ on 2 September 2006
At first glance, we might think that cells are primarily protein synthesis factories. Over half of the molecular machinery in a typical bacterial cell is dedicated to building new proteins. These include the DNA and messenger RNA, which provide the instructions, transfer RNA, which performs the translation of this information, and ribosomes, which do the major construction work. Protein synthesis also requires a flurry of protein factors to orchestrate each step. These include initiation factors that get it all started, release factors that finish each chain, and elongation factors that assist the many steps between the beginning and the end.
EF-Tu, shown here from PDB entry 1ttt, performs the important job of shepherding each transfer RNA to the ribosome, powered by a molecule of GTP. EF-Tu is the most plentiful protein in bacterial cells—typically there will be enough that every tRNA may be matched with one. It binds to a tRNA after the proper amino acid has been attached to it. Then, the complex docks into the active site of the ribosome. When the tRNA anticodon matches up correctly the mRNA codon, a signal from the ribosome causes EF-Tu to change shape and the molecule of GTP is cleaved. This causes EF-Tu to let go of the tRNA and leave, allowing the tRNA to enter into the reaction.
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