Microbiology Procedure

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Conformational Changes

	Conformational Changes - According to this theory the ribosomes undergo conformational changes during translocation. However, there is no explanation regarding the exact mechanism of these changes in translocation In eukaryotes EP-2, corresponding with EF-G of prokaryotes, catalyses the transfer of peptidyl tRNA (e.g. aa₂tRNA, aa₃tRNA etc.) from the A site to the P site. As usual the γ-phosphate of GTP is hydrolysed. When the ribosome moves about 80 nucleotides down the mRNA strand, a second ribosome may be attached to the mRNA. The same mRNA strand is now utilized bi the second ribosome to synthesize an identical polypeptide chain. In this way a series of ribosomes may associate with the mRNA to form a polyribosome.
The number of ribosomes in a polyribosome depends upon the molecular weight of the polypeptide chain synthesized. Generally there is one ribosome for every 25 to 30 amino acids in the polypeptide chain, or for 3,000 to 4,000 molecular weight. Thus the polyribosome synthesizing haemoglobin subunits consisting of about ISO amino acids contains 4 to 6 ribosomes. The subunits of myosin (MW 180,000) are synthesized by polyribosomes of about 60 ribosomes. Since an mRNA strand functions simultaneously on several ribosomes, the number of mRNA molecules required is much fewer than the number of polypeptide chains synthesized.
(ix) Synthesis of all Polypeptide chains begins at the amino (-NH2) terminal and proceeds to the carboxyl (-COOH) terminal. A polyribosome in the process of synthesizing polypeptide chains shows chains of gradually varying lengths on the different ribosomes. The shortest chains are in front of the strand and the longest chains behind. Of course, when the mRNA has passed through all the ribosomes all the polypeptide chains will be identical and of equal length.

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Protein Synthesis Part 1 Release of Deacylated tRNA Hydrolysis of GTP Locking and Unlocking Ribosome Model inchworn Theory Conformational Changes Recognition of the Termination Signal Release of the Polypeptide Chain Prokaryote and Eukaryote Release Factors Processing Polypeptide Chain Rate of Protein Synthesis Signal Hypothesis Prokaryote and Eukaryote Protein Synthesis Teminism

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