BIOL 1411 1st Edition Lecture 25Outline of Last Lecture I. Gene Expressiona. Translationb. Gene RegulationOutline of Current Lecture II. Gene Expressiona. RegulationLectureGene Regulation- Prokaryotic Gene Regulationo 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. colio E coli lives in the gut; gene expression is responsive to the cellular are external environmento 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 glucoseo 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 B-galactosideso Lactose Metabolism: the lac operon Lactose (converted to allolactose in cell) is the inducer An example of inducilble gene regulation, through transcriptionThese 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. However, as a secondary level of control lac operon is also responsive to cellular glucose levels o The lac repressor and lac operon Two separate genetic modules- A gene (i) coding for the lac repressor protein; a negative regulatorof the lac operon- Lac operon coding for 3 structural proteins needed for utilization of lactose o 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 o Regulation of the lac operon Original paradigm for negative control in prokaryotes- Repressor proteins exerts negatice control by blocking transcription when bound at the operatoro 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 transcriptiono When lactose is present- operon is turned on (=expressed) o 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 presenceof 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 CRPo 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 controlo 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 thatinteract with RNA polymerase and regulate rate of transcription Some are positive regulators- enhancers; others are negative-