Ro_Lecture16 - Lac Operon 1 Lactose and Glucose Much of the...

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1 Lac Operon
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2 Lactose and Glucose Much of the control of gene expression occurs at the transcriptional level Our understanding of transcriptional regulation comes from studies Of enzyme induction in E.coli E. Coli exhibit an extremely sophisticated regulation of enzyme Induction in response to changing environmental conditions. The primary source of food for bacteria is glucose! If both glucose and lactose are present together, glucose is utilized first. The organism will first breakdown glucose by turning on genes for enzymes that metabolize glucose. The enzymes required for lactose metabolism are shut off! Once the glucose is completely metabolized, the genes responsible for glucose metabolism are shut down. Then the genes for the enzymes involved in lactose metabolism are turned on. How does a cell turn on and off these genes? How does E. coli monitor the environment?
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3 Gene Regulation Questions were first addressed by studying genes controlling lactose metabolism in E. coli Lactose metabolism requires a b-galactosidase When only lactose is present, the genes for lactose metabolism are turned on. When all the lactose is broken down, these enzyme are shut off That is the genes coding for these enzymes are shut off
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4 Gene Regulation There are two ways you can visualize this occurring. Lactose present gene ON Lactose absent gene OFF Cells– lactose β -galactosidase 1 × low level Cells + lactose β -galactosidase 1000 × induced
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5 Gene Regulation You can classify genes in a simple way in two classes 1) Structural 2) Regulatory The structural genes are those that produce the enzyme required for lactose metabolism Permease Allows transport of lactose into the cell Galactosidase cleaves lactose into glucose and galactose Transacetylase Unknown function The regulatory genes determine whether transcription of the
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This note was uploaded on 04/15/2008 for the course BIO 105 taught by Professor Sullivan during the Fall '08 term at University of California, Santa Cruz.

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Ro_Lecture16 - Lac Operon 1 Lactose and Glucose Much of the...

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