Lecture 23 Chapter 36 Transcription and the Regulation of Gene Expression Outline Transcription in prokaryotes RNA polymerase Sites of Initiation Transcription Elongation Transcription termination Transcription Regulation the lac operon Overview of Transcription in Eukaryotes The RNAs mRNA rRNA and tRNA are all synthesized by transcription of DNA sequences rRNA But unlike mRNAs rRNAs and tRNAs are not subsequently translated into proteins DNA Telomerase RNA TRANSCRIPTION by RNA Polymerase DNA dependent mRNA TRANSLATION on Ribosome Protein tRNA Expression of Genetic Information Requires Mg2 or Mn2 Prokaryotic Molecular Biology DNA DNA Replication mRNA 5 N In Prokaryotes Transcription and Translation are Coupled Initiation site on DNA mRNA 1 mRNA 2 mRNA 3 mRNA 4 mRNA transcript Prokaryotic mRNA DNA Protein B Polycistronic mRNA Protein A Protein c Core Bacterial RNA Polymerase Core Polymerase 2 Holoenzyme Core Subunits of E coli RNA polymerase The three stages of RNA synthesis are 1 Initiation 2 Elongation 3 Termination The Subunit Recognizes and Binds to the Promoter Start site 35 17 2 10 Consensus TATAAT 5 TTGACA 1 3 The E coli RNA polymerase holoenzyme Transcription Initiation Non template coding DNA strand 5 3 35 sequence Pribnow box 17 bp UP elements The C terminal domain of alpha binds the Upstream Promoter UP element if there is one closed promoter complex RNA Pol acts as a helicase opened promoter complex RNA Pol acts as a primase transcription bubble Sigma recycles The transcription bubble RNA DNA hybrid region is 8 bps Elongation Topoisomerases pppG or pppA gyrases Strand Elongation Reaction P P P First nucleotide ppp A or pppG OH OH Phosphodiester linkage Transcription Termination Intrinsic palindrome sequence poly U on nascent RNA Extrinsic Rho dependent termination Intrinsic Termination Signal Antisense Template Intrinsic termination signal Palindrome at the end of a mRNA transcript poly U RNA hairpin Several uracyl residues Intrinsic Termination Protein factor Rho dependent termination Rho binds rut sites Rho utilization site Control of Bacterial Gene Expression lac operon Galactosidase Induction Operons allow parallel regulation of functionally related genes galactosidase permease transacetylase X Regulation of the Lac Operon transcription Glucose No lactose p o Inducer reduces the affinity of the repressor for the operator DNA Polygenic polycistronic transcript Inducers of lac operon Regulation of the Lac Operon transcription Glucose and Lactose Inducer Repressor X Positive Regulation of lac Operon by the Catabolite Activator protein CAP 61 Glucose catabolic repressor acts by cAMP Regulation of the Lac Operon transcription Lactose No glucose Activators can facilitate transcription initiation The Kornberg Arthur Roger FIGURE 18 41 Roger Kornberg right won the 2006 Nobel Prize in Chemistry for his elucidation of the molecular mechanism of eukaryotic transcription His father Arthur Kornberg who died in 2007 received the 1959 Nobel Prize in Physiology or Medicine for his work on prokaryotic DNA polymerases Biochemistry The Molecular Basis of Life 5 e Gene Expression in Eukaryotes Eukaryotes have tissue specific expression Eukaryotes have 3 RNA polymerases Eukaryotic mRNAs DNA Pre mRNA mRNA protein a single mRNA encodes a single protein Monocistronic mRNA Higher Organisms have more Introns More introns means more opportunities for alternative splicing 4 Basic Types of Alternative Splicing Spliced mRNA Pre mRNA Spliced mRNA Alternative 5 splice site Alternative 3 splice site Exon skipping or inclusion Intron inclusion Nilsen Graveley Nature 463 457 2010 Alternative Splicing creates multiple protein isoforms http www hindawi com journals jna 2012 162692 fig1 http eterna cmu edu web By playing EteRNA you will participate in creating the first large scale library of synthetic RNA designs Your efforts will help reveal new principles for designing RNA based switches and nanomachines new systems for seeking and eventually controlling living cells and disease causing viruses By interacting with thousands of players and learning from real experimental feedback you will be pioneering a completely new way to do science Join the global laboratory Learning Goals Know the steps of prokaryotic transcription Understand transcription regulation of Lac operon Be able to describe the general differences between prokaryotic and eukaryotic transcription
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