IUB BIOL-L 211 - Translation II (4 pages)

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Translation II

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Translation II


Translation Elongation and Termination

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Lecture Note
Indiana University, Bloomington
Biol-L 211 - Molecular Biology
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BIOL L211 Lecture 32 Outline of Last Lecture I Recruiting Ribosome to mRNA transcript II Initiation of Prokaryotic Translation III Initiation of Eukaryotic Translation IV Eukaryotic Translation Outline of Current Lecture I Translation Elongation II Translation Termination Current Lecture Translation II I Translation Elongation A No significant difference that we will cover between eukaryotes and prokaryotes B Major Steps 1 Codon in A site determines which tRNA is recruited and loaded 2 Amino acids are linked by a peptide bond 3 Polypeptide from tRNA in P site shifts to the charged tRNA in the A site 4 Ribosome is transferred toward 3 end of mRNA a A new codon is then in the A site b Empty tRNA is ejected via the E site 5 Repeat Until stop codon C Elongation Factor EF Tu These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute 1 EF Tu elongation factor responsible for binding and bringing charged tRNAs to A site 2 EF Tu GTP ensures tRNA binds at appropriate time 3 GTP hydrolyzes when tRNA binds correct codon which causes the release of EF Tu GDP 4 Accommodation rotation of charged tRNA into the peptidyl transferase center D Peptide Bond Formation 1 Incorrect codon anticodon pairing causes a Reduced EF Tu GTPase activity b No accommodation 2 For Peptide Bond to form correctly charged tRNA must be in A site AND have gone through accommodation 3 Bond between amino acids is called a peptide bond and is formed through a dehydration reaction loss of water 4 rRNA in large subunit catalyzes peptide bond formation 5 Protein directionality N terminus to C terminus E Elongation Factor EF G 1 Translocation Movement of tRNA from A site to P site and movement of uncharged tRNA to the E site shift down one codon 2 After peptide chain is moved to A site tRNA tRNAs shift to hybrid state their 3 Hybrid State state in which 3 ends of the tRNAs are in new positions in the large ribosomal subunit while anticodons are still bound to the codons in initial locations in the small ribosomal subunit 4 EF G GTP binds ribosome and uses GTP hydrolysis to GDP to change its conformation a tRNAs are then fully transferred to respective new sites b EF G dissociates note in both EF Tu and EF G GTP hydrolysis causes dissociation c A site is left open again II Translation Termination A Stop codon in A site triggers termination no corresponding tRNAs B Class I release factors RFs bind stop codon as opposed to tRNA and cause the release of the polypeptide chain from the tRNA in the P site 1 Prokaryotes Have DIFFERENT Class I RFs to recognize each of the three stop codons 2 Eukaryotes Have only one Class I to recognize all three stop codons C Class II release factors exchange GDP for GTP causing class I RFs to leave D GTP hydrolysis causes dissociation of class II RFs E Ribosome Recycling 1 tRNAs and mRNA are removed from ribosome 2 Ribosome breaks apart into its large and small subunits IF3 stimulates ribosome dissociation 3 Ribosome Recycling Factor RRF enters A site which has stop codon a EF G binds RRF and moves it to the P site b RRF in the P site causes release of tRNAs in BOTH P and E sites 4 RRF and EF G released from ribosome 5 mRNA released F Interpreting Stop Codons ribosome as 1 Exon Junction Complex result of splicing proteins that bind around 20 nucleotides upstream from the exon exon junctions and guide the it proceeds a EJC contact continue translating b Translation terminates when it hits the stop codon with no EJC proteins downstream G Nonsense mediated mRNA Decay 1 Degradation of mRNA with a stop codon in the improper location early in eukaryotes as splicing only occurs in eukaryotes 2 If there are EJC proteins following a stop codon proteins come and degrade mRNA 3 If there are no EJC proteins following a stop codon translation terminates

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