Chapter_30

Chapter_30 - Chapter 30 Protein Synthesis Translation is...

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Chapter 30 Protein Synthesis Translation is the Process by Which an RNA (DNA) Sequence is Converted into an aa Sequence The X-ray Structure of the Ribosome Showed that the Ribosome is a Ribozyme Bacterial Ribosome is 70 S, containing 50S Subunit: 23S rRNA 30S Subunit: 16S rRNA 5S rRNA
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Chapter 30 Read 857-880, 884-885
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tRNA Translates the mRNA Sequence into a Protein  Sequence Amino-acyl tRNA synthetase  adds specific amino acid to  specific tRNA The reaction is driven by ATP  cleavage For misincorporation  rate ε  and n residues: p = (1 –  ε )n Lower error rate than  10-4 would slow  translation
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Yeast alanyl-tRNA 76 nucleotides, sequenced in 1976 The Design of tRNA Molecules 3’-C-G-I-5’ 5’-G-C-C-3’ Anticodon: codon 1. 73-93 nucleotides 2. 7-15 “modified” nucelotides 3. ~50% base-paired 4. ψ (dihydrouracil) 5. Anticodon loop
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The 3D Structure of tRNA 1. L-shape 2. 2 continuous segments 3. Hydrogen bonding interactions in  non-helical regions 4. Protruding CCA loop 5. Anticodon loop at opposite end
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Adenylation Activates the Amino Acid Amino acid + ATP + tRNA aminoacyl-tRNA + AMP + PPi
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H 3 N COO H H O H H + - H 3 N COO H CH 3 C H 3 H + - H 3 N COO H CH 3 O H H + - How Aminoacyl-tRNA Synthetases Achieve  Amino Acid Discrimination: I Threonyl-tRNA synthetase Coordination of a zinc ion by 2  histidines and a cysteine serine valine threonin e Serine is  misincorp orated at  rate of 10- 2 to 10-3
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Proofreading by tRNA Synthetase: the  Double Sieve H 3 N COO H H O H H + - serine H 3 N COO H CH 3 O H H + - threonin e Editing site improves  misincorporation to 1 in  10-4 > 20 Å betwee n sites Usually: acylation site rejects larger aa,  hydrolitic site smaller aa Some synthetases (e. g. tyrosine) require no editing 3’CCA swings  out to switch  sites
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Recognition of tRNA by Synthetase through the  Anticodon Loop and/or the Acceptor Stem
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Chapter_30 - Chapter 30 Protein Synthesis Translation is...

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