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LECTURE 14 RNA: TRANSCRIPTION & PROCESSING kchapter 8 k announcements k key ideas k RNA k transcription in Prokaryotes k transcription in Eukaryotes
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ANNOUNCEMENTS g missed or late for quiz ? g same documentation required as for exams g no makeup… average of those you write g exam 2 … M 11.13 in class, as listed on calendar g extra tutorial help … g M 3:00 – 4:30 & F 11:00 – 12:30 in WHI 111 g extra-credit tutoring … in progress, check web page g extra-credit seminar WHI AUD F 3:30 g Dr. Juli Wade, Michigan State U. g Hormonal and Genetic Influences on Sexual Differentiation of the Zebra Finch Song System
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CH8 KEY IDEAS k 3 processes of information transfer in genetics CH8 CH7 CH9
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CH8 KEY IDEAS k translation requires transfer RNAs & ribosomes k information transfer by non-overlapping triplet code k special DNA sequences signal initiation & termination of transcription & translation k in Eukaryotes only... k mRNA transcripts are processed prior to translation k noncoding introns interrupt coding exon sequences k introns are spliced out of 1° mRNA final mRNA k DNA transcription RNA translation protein
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CH8 KEY IDEAS k transcription & translation
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RNA k DNA protein... RNA intermediate? k pulse-chase experiments with RNA precursors... pulse radioactive, chase nonradioactive, autoradiograph k synthesis of RNA in nucleus protein in cytoplasm
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RNA
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k usually single-stranded, double-stranded, complex 3D structures antiparallel k ribose sugar deoxyribose C2 HC2 H C 2 OH RNA A U A T RNA DNA k uracil pyrimidine thymine
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k classes 1. informational k mRNA:translated polypeptides 2. functional k tRNA: bind & transport amino acids k rRNA:components of ribosomes k snRNA:participate in modifying rRNA components of spliceosomes RNA
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TRANSCRIPTION IN PROKARYOTES k T2 bacteriophage infection of E. coli k pulse-chase with radiolabeled uracil (RNA-precursor) k labeled RNA recovered only immediately after pulse... rapid turnover k phage-induced RNA similar to T2 DNA... DNA RNA
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TRANSCRIPTION IN PROKARYOTES k in vitro synthesis shows RNA DNA... DNA template & complementary RNA bases k similar to DNA replication, with DNA polymerase... transcription enzyme... RNA polymerase ?
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TRANSCRIPTION k RNA synthesized from 1 or both DNA strands? k hybridization experiment k complementary DNA strands have different densities k each RNA hybridizes to only 1 DNA strand k transcription is asymmetrical
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TRANSCRIPTION IN PROKARYOTES k DNA template for mRNA transcription k note directional nature of event
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TRANSCRIPTION IN PROKARYOTES k DNA coding strand = nontemplate strand k sequence homologous to transcribed mRNA k DNA has A, RNA has U k DNA template strand mRNA
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TRANSCRIPTION IN PROKARYOTES knew mRNA grows 5' 3' kRNA pol moves along DNA template strand 3' 5' 5' 3' 5' 3' error! k genes transcribed from one but either DNA strand k transcription by complementary pairing of bases k catalyzed by RNA polymerase (RNA pol)
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TRANSCRIPTION IN PROKARYOTES kRNA pol moves along DNA template strand 3' 5' knew mRNA grows 5' 3' knormally illustrate in other direction for convenience
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TRANSCRIPTION IN PROKARYOTES k transcription of rRNA genes in Triturus nucleus
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TRANSCRIPTION IN PROKARYOTES k3 distinct stages of transcription 1. initiation 2. elongation 3. termination
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TRANSCRIPTION IN PROKARYOTES kinitiation k2 types of sequences in prokaryotic genes 1. promoter sequences signal initiation 2. coding sequences are transcribed
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TRANSCRIPTION IN PROKARYOTES kinitiation k2 regions of homology among promoter sequences kconsensus sequences = RNA pol binding sites
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TRANSCRIPTION IN PROKARYOTES kinitiation k factor binds to –10 and –35 consensus regions kinitiates melting or denaturing of DNA ktranscription begins when subunit dissociates open promoter complex k different factors recognize different DNA sequences closed promoter complex
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TRANSCRIPTION IN PROKARYOTES kelongation knew mRNA grows 5' 3' kRNA pol and transcription bubble moves 3' 5' along the DNA template strand 5' 3'
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TRANSCRIPTION kelongation knew mRNA grows 5' 3' kRNA pol moves along DNA template strand 3' 5' kribonucleoside triphosphate added to 3' end of n th base 3'3' 5'5' 5'5' 3'3'
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kelongation knew mRNA grows 5' 3' kRNA pol moves along DNA template strand 3' 5' k pyrophosphate ion released 3'3' 3'3' 5'5' 5'5' TRANSCRIPTION IN PROKARYOTES
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ktermination kRNA pol recognizes signal for chain termination k 2 mechanisms for termination in prokaryotes 1. direct termination - termination sequence TRANSCRIPTION IN PROKARYOTES mRNA 3' UTR DNA CG rich + AAA...(6+) 5' 3'
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ktermination kdirect termination, RNA pol recognizes ~40 bp terminator sequence on template kRNA forms hairpin loop kpoly-A tail bonds weak ksignal to release RNA pol k ATP-independent TRANSCRIPTION IN PROKARYOTES
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ktermination kRNA pol recognizes signal for chain termination k 2 mechanisms for termination in prokaryotes 1. direct termination - termination sequence 2. rho-dependent TRANSCRIPTION IN PROKARYOTES
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ktermination krho-dependent termination kno U-residues formed kno hairpin loop krho binds to rut site on RNA TRANSCRIPTION IN PROKARYOTES
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ktermination krho-dependent termination kno U-residues formed kno hairpin loop krho binds to rut site on RNA krho “pulls” RNA from RNA pol
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TRANSCRIPTION IN PROKARYOTES ktermination krho-dependent termination kno U-residues formed kno hairpin loop krho binds to rut site on RNA krho “pulls” RNA from RNA pol
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TRANSCRIPTION IN EUKARYOTES kdifferences because of complexity in Eukaryotes 1. RNA synthesis
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TRANSCRIPTION IN EUKARYOTES kProkaryotes: k RNA pol all types of RNA k polycistronic mRNA kEukaryotes: k RNA pol I rRNA (except 5S rRNA) k RNA pol II monocistronic mRNA, some snRNA k RNA pol III tRNA, 5S rRNA, some snRNA
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TRANSCRIPTION IN EUKARYOTES kProkaryotes: k RNA pol only kEukaryotes: k RNA pol II + general transcription factors (GTFs) mRNA DNA GTFs
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TRANSCRIPTION IN EUKARYOTES kdifferences because of complexity in Eukaryotes 1. RNA synthesis 2. RNA processing
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TRANSCRIPTION IN EUKARYOTES kProkaryotes: k no processing kEukaryotes: k processed before being transported to the cytoplasm
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TRANSCRIPTION IN EUKARYOTES kdifferences because of complexity in Eukaryotes 1. RNA synthesis 2. RNA processing 3. chromosome organization 4. split genes
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TRANSCRIPTION IN EUKARYOTES kProkaryotes: k naked DNA (nearly) kEukaryotes: k chromatin – euchromatin & heterochromatin
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TRANSCRIPTION IN EUKARYOTES k3 distinct stages of transcription 1. initiation 2. elongation 3. termination
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TRANSCRIPTION IN EUKARYOTES kinitiation kGTFs TATA sequence before RNA pol II binding k attract RNA pol II k positions complex kGTFs added after preinitiation complex k transcription bubble
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TRANSCRIPTION IN EUKARYOTES kelongation kGTFs added after preinitiation complex k transcription bubble k RNA pol II carboxyl tail domain (CTD) phosphorylated...
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TRANSCRIPTION IN EUKARYOTES k2 types of processing 1. cotranscriptional
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TRANSCRIPTION IN EUKARYOTES kcotranscriptional processing – CTD dependend k guanyltransferase adds 7'-methylguanosine “cap” to 5' end of mRNA k protects single stranded RNA from degradation
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TRANSCRIPTION IN EUKARYOTES kcotranscriptional processing – CTD dependend k splicing by spliceosomes (... stay tuned)
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TRANSCRIPTION IN EUKARYOTES ktermination k AAUAAA sequence near 3' end initiates cleavage k... by endonuclease ~ 20 bp downstream
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TRANSCRIPTION IN EUKARYOTES k2 types of processing 1. cotranscriptional 2. posttranscriptional
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TRANSCRIPTION IN EUKARYOTES kposttranscriptional processing k poly(A) polymerase adds poly(A) tail of 150-200 adenosine residues to 3' end cleavage site k complete °1 mRNA
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EUKARYOTIC RNA k°1 mRNA shortened before transport to cytoplasm kchicken ovalbumin DNA/mRNA hybrid kcoding sequences... exons
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EUKARYOTIC RNA k°1 mRNA shortened before transport to cytoplasm kchicken ovalbumin DNA/mRNA hybrid kcoding sequences... exons kintervening sequences... introns
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EUKARYOTIC RNA k°1 mRNA shortened before transport to cytoplasm kchicken ovalbumin DNA/mRNA hybrid kcoding sequences... exons kintervening sequences... introns kintrons spliced from mRNA kgenomic DNA RNA exons + introns
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ksummary... kgenomic DNA RNA exons + introns ktranscribed 1° mRNA transcript kprocessed cap & polyadenylation kspliced splicing intermediate kspliced mature mRNA TRANSCRIPTION IN EUKARYOTES
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k1 gene multiple functions by alternative splicing kmultiple gene functions in different... k tissues k developmental stages kdifferent mRNAs from same 1° mRNA transcript... e.g., -tropomyocin gene... TRANSCRIPTION IN EUKARYOTES
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k1 gene multiple functions by alternative splicing e.g., -tropomyocin gene... TRANSCRIPTION IN EUKARYOTES
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kgene splicing mechanism... ksequence homologies at exon-intron splice junctions k= consensus sequences for splicing enzymes... TRANSCRIPTION IN EUKARYOTES
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kspliceosome ksnRNA aligns sequences correctly for splicing TRANSCRIPTION IN EUKARYOTES
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ksplicing reaction kintron lariat structure kintrons excised by 2 transesterification reactions TRANSCRIPTION IN EUKARYOTES
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ksplicing reaction kintron lariat structure kintrons excised by 2 transesterification reactions ksnRNA + proteins small ribonuclear particles (snRNPs) ksnRNP + 1° mRNA transcript spliceosome kspliceosome catalyzes splicing transesterification reactions TRANSCRIPTION IN EUKARYOTES
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kself splicing mechanisms, mRNA catalyzes reaction (called ribozymes) TRANSCRIPTION IN EUKARYOTES
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kself splicing mechanisms, mRNA catalyzes reaction kspliceosome-catalyzed mechanism TRANSCRIPTION IN EUKARYOTES
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kTUTORIAL 6 QUESTIONS – CHAPTER 8
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