BIOL 1411 1st Edition Lecture 25 Outline of Last Lecture I Gene Expression a Translation b Gene Regulation Outline of Current Lecture II Gene Expression a Regulation Lecture Gene Regulation Prokaryotic Gene Regulation o Prokaryotes generally stop synthesis of a protein when it is not needed The cell can Repress mRNA transcription Hydrolyze mRNA preventing translation Prevent mRNA translation at the ribosome Hydrolyze the protein after it is made Inhibit the proteins function Energy sources in E coli o E coli lives in the gut gene expression is responsive to the cellular are external environment o Glucose of other sugars such as lactose may be present Glucose is preferred but not always available Utilization of lactose requires synthesis of proteins to take it in and break it down into glucose o Uptake and metabolism of lactose involves 3 proteins B galactosidepermease a carrier protein that moves lactose into the cell B glactosidase an enzyme that hydrolyses lactose B galactosidetransacetylase transfers acetyl groups to certain Bgalactosides o Lactose Metabolism the lac operon Lactose converted to allolactose in cell is the inducer An example of inducilble gene regulation through transcription These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute o o o o However as a secondary level of control lac operon is also responsive to cellular glucose levels The lac repressor and lac operon Two separate genetic modules A gene i coding for the lac repressor protein a negative regulator of the lac operon Lac operon coding for 3 structural proteins needed for utilization of lactose The lac operon The structural genes needed to utilize lactose are adjacent on the E coli chromosome share a single promoter and are encoded on a single transcript different sites of translation initiation The operon is under coordinate control from the Promoter the region of DNA where RNA polymerase binds and initiates transcription Operator the region of DNA between the promoter and the structural genes that is bound by the lac repressor A repressor protein made by a different regulatory gene called lac i binds to the operator to block transcription of the operon when lactose is absent Regulation of the lac operon Original paradigm for negative control in prokaryotes Repressor proteins exerts negatice control by blocking transcription when bound at the operator o Repressor able to bind in the absence of the inducer allolactose and operon is turned off repressed Inducer changes repressor protein so that is unable to bind at the operator operon available for transcription o When lactose is present operon is turned on expressed E Coli lac operon also an example of transcriptional activation Catabolite repression a separate mechanism for controlling transcription of the lac operon Cells respond to the glucose concentration in their environment Glucose is the preferred sugar If glucose is abundant there is no need to utilize lactose transcription of lac operon structural genes is kept low in presence of lactose If glucose is low it can be obtained through utilization of more complex sugars such as lactose Glucose concentration is measured indirectly by the cell Low glucose high concentration of cAMP High glucose low concentration of cAMP cAMP interacts with an activation protein call CRP o Transcriptional regulation in E coli Genes the encode prteins that are involved in the same metabolic pathway are organized in operons Two kinds of bacterial operons Inducible cataboli operons lac operon o Substrate the inducer for a catabolic enzyme binds to repressor and changes it so it cannot bind the operator transcription ON Repressible anabolic operons trp operon o End product of the anabolic pathway acts as a corepressor to allow repressor to bind operator and repress transcription transcription OFF Transcriptional control o Transcription factors regulatory proteins must assemble on the chromosome before RNA polymerase is recruited to the promoter o TFIID binds to the TATA box other transcription factors bind to form a transcription complex o Regulation of Eukaryotic Gene Expression Transcription factors act at eukaryotic promoters regions of DNA where RNA polymerase binds and initiates transcription 2 important sequences Recognition sequence recognized by RNA polymerase TATA box where DNA begins to denature and expose the temple strand o Enhancers and Silencers Besides the promoter other DNA sequences bind regulatory proteins that interact with RNA polymerase and regulate rate of transcription Some are positive regulators enhancers others are negative silencers