Lecture 23 Chapter 36 Transcrip on and the Regula on of Gene Expression Outline Transcrip on in prokaryotes RNA polymerase Sites of Ini a on Transcrip on Elonga on Transcrip on termina on Transcrip on Regula on the lac operon Overview of Transcrip on in Eukaryotes The RNAs mRNA rRNA and tRNA are all synthesized by transcrip on 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 Gene c Informa on 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 Prokaryo c 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 Ini a on 2 Elonga on 3 Termina on The Subunit Recognizes and Binds to the Promoter Start site 35 17 2 10 TTGACA Consensus TATAAT 5 1 3 The E coli RNA polymerase holoenzyme Transcrip on Ini a on 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 transcrip on bubble RNA DNA hybrid region is 8 bps Elonga on Topoisomerases pppG or pppA gyrases Strand Elonga on Reac on P P P First nucleo de ppp A or pppG OH OH Phosphodiester linkage Transcrip on Termina on Intrinsic palindrome sequence poly U on nascent RNA Extrinsic Rho dependent termina on Intrinsic Termina on Signal An sense Template Intrinsic termina6on signal Palindrome at the end of a mRNA transcript poly U RNA hairpin Several uracyl residues Intrinsic Termina on Protein factor Rho dependent termina on Rho binds rut sites Rho utiliza on site Control of Bacterial Gene Expression lac operon Galactosidase Induc6on Operons allow parallel regula on of func onally related genes galactosidase permease transacetylase X Regula on of the Lac Operon transcrip on Glucose No lactose p o Inducer reduces the a nity of the repressor for the operator DNA Polygenic polycistronic transcript Inducers of lac operon Regula on of the Lac Operon transcrip on Glucose and Lactose Inducer Repressor Posi ve Regula on of lac Operon by the Catabolite Ac vator protein CAP 61 Glucose catabolic repressor acts by cAMP Regula on of the Lac Operon transcrip on Lactose No glucose Ac vators can facilitate transcrip on ini a on The Kornberg Arthur Roger FIGURE 18 41 Roger Kornberg right won the 2006 Nobel Prize in Chemistry for his elucida on of the molecular mechanism of eukaryo c transcrip on His father Arthur Kornberg who died in 2007 received the 1959 Nobel Prize in Physiology or Medicine for his work on prokaryo c DNA polymerases Biochemistry The Molecular Basis of Life 5 e Gene Expression in Eukaryotes Eukaryotes have ssue speci c expression Eukaryotes have 3 RNA polymerases Eukaryo c 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 Alterna ve Splicing creates mul ple protein isoforms hip www hindawi com journals jna 2012 162692 g1 hip eterna cmu edu web By playing EteRNA you will par cipate in crea ng the rst large scale library of synthe c RNA designs Your e orts 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 interac ng 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 prokaryo c transcrip on Understand transcrip on regula on of Lac operon Be able to describe the general di erences between prokaryo c and eukaryo c transcrip on
View Full Document
Unlocking...