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LECTURES 30-32.docx

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University of Waterloo
BIOL 308
Bruce Wolff

LECTURES 30321 What is the role of ShineDalgarno sequenceprokaryotesit is the conserved sequence 813 nucleotides upstream the start codon in prokaryotes that is complementary to the 16S rRNA in the small 30S subunit of the ribosomealso called the ribosomal binding site RBS this sequence enables the ribosome to position itself correctly with respect to the start codon at P site of first methionine 5AGGAGGU32What is the role of Kozak sequenceEukaryotes Kozak sequence is a consensus sequence in eukaryotes that has the AUG embedded in it as 5CC AG CC AUG G3this sequence is recognized by the 40S subunit which already has initiator tRNA bound which binds to the methyl cap and scans mRNA for the Kozak sequencewhile AUG is the start codon it must be present within the right context for proper binding of the ribosome to the mRNA 3What are the major differences in initiation of translation between eukaryotes and prokaryotes remember first AA and the way mRNA and tRNA bind to ribosomestranslation initiation in eukaryotesoAUG embedded in Kozak sequenceo40 S subunit recognizes 5cap and scans until AUG in a Kozak context is foundotRNA comes to ribosome before addition of mRNA translation initiation in prokaryotesoAUG downstream from ShineDalgarno sequenceoribosomes 16S rRNA complementary to SD and base pairsotRNA with fMet is added to complex after addition of mRNA4Describe in detail events during initiation of the Eukaryotic or Prokaryotic translation a Prokaryotic Initiation1IF3 binds to free 30S subunit prevention of binding of 50S subunit2IF1 binds prevents potential binding of tRNA to A site3IF2 GTPase complexes with GTP and binds4mRNA binds to 30S subunit through interaction of ShineDalgarno sequence with 16S rRNA5Initiator tRNA binds anticodoncodon base pairing to P site6This forms the 30S initiation complex750S subunit binds8This displaces IF1 and IF2 IF3and GTP is hydrolyzedenergy consuming step 9This forms the 70S initiation complexb Eukaryotic Initiation1Free 40S subunit complexes with eIF3 large proteinand eIF1A to keep it apart from 60S subunit2Ternary complex forms ie initiator tRNA eIF2 and GTP3This binds to 40S forming the 43 preinitiation complex
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