In elongation - dipeptide and the initiator tRNA being...

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In elongation The first step is the binding of a second charged tRNA that base pairs specifically with the second codon. EF-Tu and GTP bind the charged tRNA and help to align the tRNA in the A site . When base pairing of the anticodon-codon occurs, GTP is hydrolyzed and EF-Tu + GDP are released. The binding of the tRNA to the ribosome is possible because the large subunit of the ribosome contains several sites that tRNAs can occur in and bind to by its D loop and T psi C loop: o the P ( peptidyl ) site occupied at the moment by the initiator tRNA, o the A ( aminoacyl or acceptor) site occupied at the moment by the second tRNA, o and an E ( exit ) site currently unoccupied. The second step is the formation of a peptide bond between the two amino acids, a process catalyzed by the enzyme peptidyl transferase which is associated with the large ribosomal subunit . The result is a transfer of the N- formylmethionine to the second tRNA in the A site which carries now a
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Unformatted text preview: dipeptide and the initiator tRNA being uncharged in the P site. The third step is the translocation of the ribosome to move 3 bases or 1 codon along the mRNA. This translocation also positions the initiator tRNA to the E or exit site , the second tRNA with the dipeptide to the P site and leaves the A site unoccupied but with the third codon exposed. Translocation is catalyzed by the elongation factor EF-G . The G indicates that this factor uses the energy gained from the hydrolysis of GTP for translocation to occur. Finally a third tRNA is escorted by EF-Tu to the A site and the anticodon base pairs specifically with the codon. This binding triggers the release of the initiator tRNA from the E site and allows the complex to be ready for another round of peptide bond formation, translocation and codon-anticodon base pairing (and so on)....
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This document was uploaded on 11/03/2011 for the course BIOLOGY MCB2010 at Broward College.

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