Chapter 14 Control of Gene Expression.docx

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University of Toronto Scarborough
Biological Sciences
Effiette Sauer

Chapter 14 Control of Gene Expression141 Prokaryote Gene ExpressionWe usually say the gene is turned on we mean that its mores likely to be transcribed actively In bacteria we can turn on a set of genes at the same time that all respond to the same signal by putting genes all in a row on the chromosome and turning on transcription from a single operon and transcribing all the genes as a single RNA142a Eukaryote Gene Regulation LevelsThere is transcriptional posttranscriptional translational posttranslational regulation142b Promoter Immediately upstream of the transcription unit is the promoter regionoften the TATAAA boxRNA polymerase II itself cannot recognize the promoter sequence Instead proteins called transcription factors bind to the TATA box and then RNA polymerase II locates the promoterPromoter Proximal region is upstream from the promoter region regulatory proteins bind to it and inhibit or enhance transcription Enhancer more upstream from the proximal region regulatory proteins bind to it and inhibit or enhance transcriptionActivation of Transcription o General Transcription Factor bind to the promoter in the area of the TATA boxo Activators regulatory proteins that play a role in positive regulatory system that controls the expression of one or more genes Directly binds to transcriptional factors to stimulate transcription initiation so many more transcripts are synthesized in a given timeo Coactivators large multiprotein complex that forms a bring between the activators of the enhancer and the proteins at the promoter and promoter proximal regions creating a loopStimulates transcription to its maximum rateRepression of Transcriptiono Repressors oppose the effect of activators thereby blocking or reducing the rate of transcriptiono Repressors bind to the same regulatory sequence to which activators bind often the enhancer preventing activators from binding to the site o Corepressors act the same as the coactivators and create a lope that inhibits initiation of transcription Combination Gene Regulation o If activators bind both to the regulatory sequences in the promoter proximal region and to the enhancer transcription is activated maximally o If a repressor binds to the enhancer and an activator binds to the promoter proximal element the amount of gene expressed depends upon the relative effects of the two regulatory proteinso Combinatorial Gene Regulation combing a few regulatory proteins particular ways the transcription of a wide array of genes can be controlled
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