12-1-08_Translation_Control_Gene_Expression

12-1-08_Translation_Control_Gene_Expression - Found in...

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Found in translation: Review From the Soviet Weekly: There will be a Moscow Exhibition of Arts by 15,000 Soviet Republic painters and sculptors. These were executed over the past two years. In a Rome laundry: Ladies, leave your clothes here and spend the afternoon having a good time.
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Announcements Written Assignment 2 due Friday, December 5, at noon. Papers must be submitted through Turnitin, and a hardcopy must also be printed that matches the Turnitin document.
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Another way to look at information flow… What does this mean? If we know the sequence of a gene (DNA) we can deduce the sequence of the protein DNA -> RNA uses complementary base pairs RNA -> protein is not complementary - translation needs a special intermediate (tRNA) and a protein-RNA complex called the ribosome
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Codons: What a bunch of degenerates! comprised of 3 consecutive nucleotides written 5’ to 3’ 4 nucleotides (U, C, A, G) so there are 4 3 (or 64) codons 3 codons signal for “stop” (stopping translation) So… there are 64 - 3 = 61 different codons for amino acids Remember, there are 20 amino acids… so some amino acids must be encoded by more than one codon = the code is “degenerate”
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AUG nearest the 5’ end signals the start site 5’ - UGAUGCCCACC… The first 3 codons in the open reading frame (or 1st AUG near the 5’ end codes for the N- terminus of the polypeptide chain
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Stopping translation 5’ - UGAUGCCCACCUGAUC - 3’ Let’s look a little further down that mRNA sequence (the original stretch of RNA is underlined)… Recall, three of the codons do not encode aa’s, they code for STOP. The three stop codons are: UAA, UGA, UAG. Where do we stop? NO YES
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mRNA codon universal decoder chart tRNAs have anti-codons that are complementary See Figure 11.41 on page 466 of Karp.
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Getting the tRNA ready for translation AA’s are added onto the free 3’ OH of tRNA This process is called “charging” Catalyzed by aminoacyl-tRNA- synthetases (cytoplasmic) A synthetase can charge more than one tRNA -O-P-O-C-C-NH 2 O O O = R - H
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Simplified view of the ribosome E
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Summary of initiation in prokaryotes or eukaryotes Small subunit binds to mRNA bound in a complex Initiation factors bind to small subunit One factor is bound with GTP (IF2-GTP in prok. or eIF2-GTP in euk.) rRNA recognizes AUG of mRNA 5’ → 3’ tRNA-Met binds IF2-GTP and small subunit tRNA-Met enters P site GTP hydrolyzed, large subunit binds, and IF2-GDP (or eIF2-GDP) released.
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Elongation Ala Met U A C C G G 5’ - G C C A C C A U G G C C U G A - 3’ 5’ 5’ next tRNA binds A site peptide bond forms P site A site
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Details of elongation: A site entry tRNA entry into A site: tRNA-EF-GTP (e longation f actors: euk’s eEF1, pro’s Tu) only traps tRNA with complementary anti-codon GTP hydrolysis -> adjusts aa-tRNA positioning EF-GDP released
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Details of elongation: peptide bond •amino group of aa-tRNA 2 binds carboxyl group of aa-tRNA
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12-1-08_Translation_Control_Gene_Expression - Found in...

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