Describes the steps of translation initiation: What is the first tRNA to bind and where does...

Describes the steps of translation initiation: What is the first tRNA to bind and where does it bind? What is the role of IF3? Now describe elongation in prokaryotes - what occupies each of the A, P and E sites during elongation. What are the roles of Ef-Tu and Ef-G? Where is energy spent in the elongation process?

Expert Solution

Ans) The first tRNA or the initiator tRNA binds to the P site of the small subunit of the ribosome.The initiator tRNA is brought to the P site by the IF-2-GTP. The role of IF3 is to block the E site of the small subunit (30S) of the ribosome so that the initiator tRNA should enter only the P site.IF3 also helps to prevent the binding of the larger subunit (50S) of the ribosome to the smaller subunit before the initiator tRNA has properly bound to the P site of the ribosome.After initiator tRNA has been placed to the P site of the ribosome, IF-1,IF-3 are released and IF-2-GTP is also converted to IF-2-GDP and the IF-2 is also released. After the P site is occupied by the initiator tRNA, Ef-Tu-GTP will bind to the aminoacyl tRNAs 3' end and bring it to the A site of the ribosome.Now,the tRNA present at the P site will form peptide bond with the amino acid present on the tRNA at A site.This process is known as transpeptidation and is catalyzed by peptidyl transferase.After the peptide bond formation,the tRNA at the P site will move to the E site and tRNA having the growing polypeptide chain at the A site will move to the P site so that vacant A site is produced for the next cycle to begin.Now,again the next aminoacyl tRNA will be brought to the A site.The tRNA present at P site will form peptide bond with the tRNA present at A site.Now all the sites are occupied and the tRNA at the E site should be removed.So the mRNA will move one codon ahead and this energy is provided by EF-G.This process is known as translocation.Movement of ribosome is always in 5' --> 3' direction.So,the energy is spent for translocation and also in regenerating the GTP for Ef-Tu for the nexy cycle to begin by Ef-Ts.

gladiator answered 2 years ago

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