lecture10 - Biology 172 Lecture 10: Friday, May 28, 2010...

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Lecture 10: Friday, May 28, 2010 Biology 172 Today’s Outline Announcements Bacterial Gene Expression - Overview -Lac operon - Monod’s expt - Operons - Negative Regulation - Catabolite Repression
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Control gene expression at these levels DNA RNA Protein Replication Transcription Translation Protein* Post-translation Gene Expression
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Gene Expression Regulating the amount of active gene product (protein) by: Control of gene expression at the level of transcription Control of at the level of translation Post-translational control
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Not all genes are regulated……. Constitutive expression = gene product made continuously Regulated expression = gene product made on demand; expression can be induced or repressed
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Regulation of Gene Expression in Prokaryotes
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E. coli cell
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Catabolic Metabolism Glucose = preferred carbon source for E. coli . Uses lactose only when glucose is depleted. E. coli must transport lactose into the cell, where it can be cleaved by the enzyme β -galactosidase to produce glucose and galactose.
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Metabolizing Lactose―A Model System Jacques Monod found that β-galactosidase not produced in E. coli cells grown in a medium containing glucose β-galactosidase is only produced in a medium containing lactose
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Figure 17-2b-setup
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Figure 17-2c-results
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Metabolizing Lactose―A Model System Jacques Monod found that β-galactosidase not produced in E. coli cells grown in a medium containing glucose OR glucose and lactose β-galactosidase is only produced in a medium containing lactose and no glucose
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Results E. coli produces high levels of β-galactosidase only when lactose is present lactose acts as an inducer— a molecule that stimulates the expression of a specific gene.
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Isolate and Analyze Mutants
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Genetic screening unmutagenized cells mutagenized cells Mutant that can’t utilize lactose as a carbon source 10 5 cells mutagen each cell has a different mutation How to find the needle in the genetic haystack? Which mutations effect lactose utilization?
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Replica plating allows identification of genes essential to utilize lactose ~5000 colonies/plate At the end, pick colonies that grow on glucose but not on lactose
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Three classes of E. coli mutants defective in lactose metabolism isolated : lacZ , lacY , and lacI RESULTS
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E. coli β -Galactosidase Galactoside permease Lactose Plasma membrane Glucose Galactose Two proteins are critical for E. coli to use lactose and one is critical for regulation of their expression Section of E. coli chromosome lacl product lacl β -Galactosidase lacZ product lacY product lacZ lacY Galactoside permease Far away on the chromosome
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Many genes in Prokaryotes are organized into OPERONS
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What is an Operon? Portion of DNA including a set of genes involved in a
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This note was uploaded on 09/13/2010 for the course 172 bio taught by Professor Raji during the Spring '10 term at University of Michigan.

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lecture10 - Biology 172 Lecture 10: Friday, May 28, 2010...

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