110C LEC 13 Translation 2

110C LEC 13 Translation 2 - BCH 110C LECTURE 13 Translation...

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BCH 110C LECTURE 13 Translation 2 Lodish 6 th ed. Chapters 3.2, 4.4, 8.4 pages 347-350
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Selection of eukaryotic translation initiation site
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Formation of the 80S Initiation Complex The 60S subunit joins the 40S initiation complex GTP bound to eIF5 is hydrolyzed Initiation factors depart Functional 80S initiation complex with the initiator tRNA in the P site is ready for elongation
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There are 3 sites in the 80S complex P site (peptidyl site) where Met-tRNA i Met is bound. A site where all subsequent aminoacyl-tRNA are first bound. E site (exit site) for used tRNAs from the P site after growing peptide transferred to the tRNA in the A site.
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Complex of the next aminoacyl-tRNA, EF1 α •GTP delivered to A site
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GTP hydrolyzed, conformational change
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Peptide bond formed
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Peptide bond formed Nucleophilic attack by unshared electrons of amino nitrogen in the A site on the carbonyl carbon of the peptidyl-tRNA The amino acid (or peptide) on "old" aminoacyl-tRNA is transferred to the amino terminus of the "new" one The tRNA in the A site is now the peptidyl-tRNA . Peptidyl-transferase catalyzes peptide bond formation . Peptidyl-transferase is a part of the 28S rRNA NOTE : EF1a does not interact with tRNA i Met . Therefore, this tRNA is never delivered to an internal AUG
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Translocation Hydrolysis of GTP (from EF2-GTP) Uncharged tRNA moves to the E site and exits the ribosome The mRNA moves three nucleotides putting a new codon in the A site The peptidyl-tRNA moves from the A to the P-site A new tRNA-EF-1 α -GTP enters the A site
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Termination at stop codons requires release factors No tRNA for the UAG, UAA or UGA stop codons Releasing factors (proteins shaped like tRNA) bind to these codons. When bound they promote hydrolysis of the peptide from the last tRNA in the P site Subunits dissociate and are reused
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Recycling of ribosomes on circular polysomes
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Polysomes: Multiple ribosomes translate an mRNA 10-100 ribosomes per mRNA
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Eucaryotes 1. Met-tRNA i (not formylated) 2. Mono- cistronic mRNA (one coding sequence) 3. Bigger, more complex ribosomes
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This document was uploaded on 05/26/2011.

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110C LEC 13 Translation 2 - BCH 110C LECTURE 13 Translation...

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