BCH Exm 3,5 - Crick's Central Dogma Part III Translation Fig 10-1 p.241 Chain Elongation Chain elongation begins with the addition of a second

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Fig. 10-1, p.241 Crick’s Central Dogma, Part III: Translation
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Chain Elongation Chain elongation begins with the addition of a second amino acid specified by the mRNA to the 70S initiation complex The P site on the ribosome is the one initially occupied by the fmet-tRNA fmet The second aminoacyl-tRNA binds at the A site The elongation factor EF-Tu (a GTPase) guides the aminoacyl-tRNA into the A site, and aligns the anticodon with the mRNA If the codon:anti-codon match is correct, EF-Tu hydrolyzes GTP to GDP plus Pi and a change in conformation dissociates it from the tRNA The elongation factor EF-Ts is a guanine nucleotide exchange factor and catalyzes the dissociation of GDP from EF-Tu - thereby freeing up EF-Tu to bind another GTP
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Fig. 12-12, p.313 fmet-tRNA fmet in the P site ala-tRNA Ala in the A site
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Fig. 12-13, p.314 Chain Elongation - Peptide Bond Formation A peptide bond is formed in a reaction catalyzed by peptidyl transferase , a component of the 50S ribosome Peptidyl transferase is the primary RNA enzymatic component of the ribosome The α -amino group of the amino acid in the A site performs a nucleolytic attack on the carbonyl-C of the amino acid linked to the tRNA in the P site This reaction is facilitated when a purine moiety on the 23S rRNA abstracts a proton This results in the generation of a dipeptidyl-tRNA in the A site and a tRNA with no amino acid (an uncharged tRNA) at the P site
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Chain Elongation - Translocation Before another amino acid can be added to the growing peptide chain, a translocation reaction must take place The uncharged tRNA moves from the P site to the E site, from which it is subsequently released The peptidyl tRNA moves from the A site to the vacated P site The ribosome shifts downstream along the mRNA This translocation step is facilitated by another elongation factor EF-G , similar to EF-Tu, hydrolyzes GTP to GDP plus Pi A new aminoacyl-tRNA can then be moved into the A site ( facilitated by the hydrolysis of GTP by the EF-Tu GTPase elongation factor ) These steps are repeated until a translation STOP signal is reached
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Fig. 12-12, p.313 Uncharged tRNA in the P site Peptidyl tRNA moves to the P site
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Chain Termination A STOP signal UAA, UAG, UGA, is required for translation termination These codons are not recognized by any tRNAs STOP codons are, however, recognized by release factors
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This note was uploaded on 04/30/2008 for the course BIO 311 taught by Professor Martin,howlett during the Spring '08 term at Rhode Island.

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BCH Exm 3,5 - Crick's Central Dogma Part III Translation Fig 10-1 p.241 Chain Elongation Chain elongation begins with the addition of a second

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