lec.13&14.translation

lec.13&14.translation - G Structures of tRNAs(a...

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Structures of tRNAs (a) tRNAs are 73~93 nucleotides long. (b) Contain several modified nucleotides. (c) The anticodon loop and the 3’ CCA of the acceptor stem.
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Two-step decoding process for translating nucleic acid sequences in mRNA into amino acid sequences in proteins The first step is mediated by the aminoacyl-tRNA synthetase, which couples a particular amino acid to its corresponding tRNA molecule at the 3’ end of tRNA (via a high-energy ester linkage with the 2’ or 3’-hydroxyl group of the terminal adenosine). The anticodon of the aminoacyl-tRNA forms base pairs with the appropriate codon on the mRNA during the second step. An error in either step would cause the wrong amino acid to be incorporated into a protein chain.
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(a) One synthetase exits for each amino acid. (b) Each synthetase usually recognizes only one tRNA. The synthetases make multiple contacts with the tRNAs and they recognize the shape rather than just the anticodon loop sequences of tRNAs. (c) Proofreading by hydrolysis of an incorrect aminoacyl-AMP, which is induced by the entry of a correct tRNA. (a) ATP + amino acid aminoacyl-AMP (enzyme-bound intermediate) + PPi (b) Aminoacyl-AMP + tRNA aminoacyl-tRNA + AMP
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The X-ray structure of E. coli Glutaminyl-tRNA synthetase complex. The tRNA and ATP are shown in skeletal form with the tRNA sugar-phosphate backbone green, its bases magenta, and the ATP red. The protein (aminoacyl tRNA synthetase specific for Gln) is represented by a translucent cyan space-filling model that reveals the buried portions of the tRNA and ATP. Note that both the 3’ end of the tRNA ( top right ) and its anticodon bases ( bottom ) are inserted into deep pockets in the protein. [Based on an X-ray structure by Thomas Steitz, Yale University.]
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Glutaminyl-tRNA synthetase complex. The structure of this complex reveals that the synthetase interacts with base pair G10:C25 in addition to the acceptor stem and anticodon loop.
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A comparison of the structure of prokaryotic and eukaryotic ribosomes. Ribosomal components are commonly designated by their “S values,” which refer to their rate of sedimentation in an ultracentrifuge. Despite the differences in the number and size of their rRNA and protein components, both prokaryotic and eukaryotic ribosomes have nearly the same structure and they function similarly.
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Low-resolution structure of E. coli 70S ribosome based on cryo- EM studies
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X-ray structure of T. thermophilus 70S ribosome
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This note was uploaded on 03/08/2010 for the course MCB 110 taught by Professor Alber,zhou,nogales during the Fall '07 term at Berkeley.

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lec.13&14.translation - G Structures of tRNAs(a...

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