lecture23 - First Step in Elongation Second aminoacyl tRNA...

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First Step in Elongation • Second aminoacyl tRNA binds to complex of EF-Tu bound to GTP • aa-tRNA/EF-Tu/GTP binds to A site of 70S initiation complex •GTP is hydrolyzed •EF-Tu/GDP complex released and Ef-Tu/GTP is regenerated A U G P A 5’ 3’ fMet U A C AA 2 E
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2nd Step in Elongation Peptide Bond Formation N-formylmethionyl group from tRNA in P site to amino group of 2nd aminoacyl tRNA in A site Peptide bond formation catalyzed by peptidyl transferase = 23S rRNA --23S rRNA acts as ribozyme --Harry Noller (1992) End up with dipeptidyl tRNA in A site and deacylated (uncharged) tRNA in P site A U G P A 5’ 3’ fMet U A C AA 2 A U G P A 5’ 3’ U A C AA 2 fMet E E
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3rd Step in Elongation Translocation Ribosome moves one codon in 3’ direction along mRNA -requires EF-G/GTP and GTP hydrolysis Dipeptidyl tRNA moves from A site to P site Deacylated tRNA in P site moves into E site Deacylated tRNA exits E site Process continues A U G P A 5’ 3’ U A C AA 2 fMet P A 5’ 3’ AA 2 fMet U A C E
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• termination codon occupies A site 3 release factors -RF1 recognizes UAG & UAA -RF2 recognizes UGA & UAA -RF3 function unknown • Either RF1 or RF2 bind to termination codon and induce peptidyl transferase to transfer polypeptide chain RF factors catalyze -hydrolysis of terminal peptidyl bond -release of free polypeptide and last tRNA -dssoiation of 70S into subunits Termination of Translation P A 5’ 3’ U A G E fMet RF1
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lecture23 - First Step in Elongation Second aminoacyl tRNA...

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