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BIO206 Term test 3 potential questions.docx

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University of Toronto Mississauga
George S Espie

BIO206 Term test 3 potential questions TUTORIAL 5 try to make a diagram which shows all the factors involvedfor all steps and label the major complexes like preinitiation initiation httpbassbioucieduhudelbs99alecture21lecture24html httpbiologykenyoneducoursesbiol114Chap05Chapter05htmlhttpenwikipediaorgwikiGeneticcodeStart2FstopcodonsInitiation in euk stage 1 Initiatior tRNA MettRNA and eIF2GTP come together at 40S subunit mRNA with eIF4GeIF4E at 5 and other eIFs euk have more than 10 bind to 40S Stage 2 When eIF4E is recognized by initiator tRNA the kozak consensus seq GCCAGCCAUGG increases ribosomal recognition of AUG Stage 3 ATP is used for movement of 40S eIF2 dissociateds when GTP is hydrolyzed and 60S binds with 40S to form the 80S initiation complex Initiation in prok stage 1 IF1IF3 assemble with 30S Stage 2 IF2fMettRNAmRNA assemble on 30S 16S rRNA base pairs with shine dalgarno sequence to identify the start site tRNA charged with Nformylmethionine looks for AUG the start codon forming the 30S initiation complex Stage 3 IF3 is released as 50S subunit binds with 30S and once the 70S initiation complex is formed other initiation factors IF1IF2 are released Elongationstage 1 EFTueEF1alpha assemble aatRNA at Asite if anticodon matches determined by decoding centre at Asite GTP is hydrolyzed and elongation factor is released and its conformation change causes aatRNA to be positioned at peptidyl transferase centre of 50S60S this centre is where aa of Asite tRNA is close to growing polypeptide chain on Psite 23S28S catalyze the peptide bond formation bw aa of tRNA at asite and growing polypeptide chain of tRNA at psite The tRNA at pSite is deacylated and growing peptide is at E site EFGeEF2 uses GTP hydrolysis to ratchet 2 subunits so large subunit moves over to next codon and tRNA at A site moves to Psite and deacylated tRNA at Psite moves to E site and the next new codon at Asite is ready for the next EFTUeEF1alpha EFTseEF1 recylces the elongation factors so they can be used again when I say ratchet 2 subunits I mean promoting translocation stage 1 is binding aatRNA stage 2 promoting translocation stage 3 recylding elongation factors The 4 steps are binding charged tRNA formation of peptide bond 50S60S moves 3 bases down to 3 and 30S40S aling with large subunit Termination UAA UAG UGA are stop codons that dont have matching anticodon tRNAs RF1 RF2 R3 are protein release factors that have 3 adjacent aa tripeptide instead of ribonucleotide anticodon to aling stop codon in A site Their shape mimics aatRNAEFTu The inexact fit precludes formation of peptide bond and idnuces peptidyl transferase centre to hydrolyze H2O and separate polypeptide chain from psite In prok RF1 recognizes UAA UAG RF recognizes UAA UGA RF3 i s associated with GTP binding In euk eRF recognizes all three stop codons 1 ribosome per 80 nucleotides What is the relationship bw cAMP and carbohydrate in the atmosphere ofthe cellokay so first CAP and cAMP are proteins in the positive regulation of the lac operon CAP and cAMP both have to be bound together to be able to bind to the CAP site on DNA without cAMP CAP cannot bind to CAP site on DNA and if CAP does not bind the it wont be able to enhance transcription like it enhances transcription in the sense that it causes the RNA Polymerase to bind more strongly to the DNAthis means that more transcripts are produced which means more translated and in the end you are making more protein now levels of glucose has an impact on the production of cAMP cAMP stands for cyclic AMP cAMP is produced by the enzyme adenylyl cyclase which converts ATP to cAMP how ever if glucose is present glucose binds to adenylyl cyclase and inhibits its function and so cAMP is not produced and therefore CAP cannot bind to the CAP site on DNA What are the 4 steps of elongation in prokeuk the general four steps for elongation are 1 the binding of charged tRNA then 2 forming of the peptide bond then 3 the movement of large subunits 3 bases downstream 3 and then 4 the final movement of the small subunits so that they align with the large subunitsthese four steps are repetitive
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