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Chapter 16 Control of Gene Expression
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Topics to discuss DNA binding proteins Prokaryotic gene regulation –Lac operon –Trp operon Eukaryotic gene regulation Today’s lecture
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6 groups of DNA-binding regulatory proteins have been identified
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Prokaryotic Gene Regulation Nutritional enviroment and a bug’s growth!
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Operons Operons provide coordinate expression
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A model operon
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Now let’s look at 2 groups of operons Negative inducible operons Negative repressible operons
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INDUCIBLE Negative inducible operon
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Turned on
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repressor
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Now let’s look at 2 specific operons The Lactose operon The Tryptophan operon
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Francois Jacob and Jacques Monod 1961 Studied lactose metabolism in prokayotes J. Monod Won the Nobel Prize in 1965
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Sources of prokaryotic energy 1. Disaccharide 2. Monosaccharide Lactose Glucose
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Building the lac operon
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ZYAOP I Lac Operon and Proposed Arrangement with control I gene Not technically part of the “operon”
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Negative inducible operon
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Conditions: No glucose but lactose is present
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Lactose Metabolism Requires Coordination of all these genes!
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Laboratory Exercise: Mutational Analysis of the lac operon
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Try out your ability to reason through the questions.
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Predict if you expect to obtain the proteins from the lacZ and lacY genes IF certain mutations are present in the operon.
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The next three slides are the “key” to the mutations.
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Mutational Key: Any + means wildtype. Any – means mutant. Two other mutants: “O c and I s ” I - cells synthesize full levels in the presence or absence of inducer- Transcription Turned ON. Inhibitor cannot bind to DNA P - the DNA promoter mutation : cannot bind RNA polymerase Transcription OFF I s super-suppressors can bind DNA but not inducer. DNA and Transcription Turned OFF. O c is an DNA mutation: repressor cannot bind. Transcription ON.
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Examples Allolactose CANNOT BIND DNA binding site I - = DNA binding site mutated, prevents binding, allows transcription I s =the Super-repressor VERSUS
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Next: 3 important terms of DNA control. Constitutive activity Trans acting Cis acting
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LactoseNo lactoseLactose I+P+O+Z+Y+I+P+O+Z+Y+ - + I-P+O+Z+Y+I-P+O+Z+Y+ I+P-O+Z+Y+I+P-O+Z+Y+ I+P+OcZ+Y+I+P+OcZ+Y+ I + P + O + Z - Y - / I - P + O + Z + Y + I + P + O c Z + Y - / I + P + O + Z - Y + I + P + O c Z - Y + / I - P + O + Z + Y - I S P + O + Z + Y - / I - P + O + Z - Y + I + P - O c Z + Y + / I + P + O + Z - Y - Β-galactosidasePermease No Lactose 1 2 3 4 5 6 7 8 9 - +
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Negative inducible operon
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Question: what happens when both lactose and glucose are present together in the same cell?
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To answer this question you first need to understand this reaction Adenylyl cyclase Cyclic AMP ATP Glucose may inhibit this enzyme catabolite activator protein + (helix-turn-helix)
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cAMP and glucose levels are inversely proportional.
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The promoter needs to be in an ideal conformation for RNA polymerase.
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How CAP and cAMP affects the promoter END of PART I
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Trypthophan Operon
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5 genes involved in the synthesis of the amino acid trypthophan
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Negative repressible operon
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2 shapes to the mRNA
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attenuation
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Eukaryotic Gene Regulation
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Do eukaryotes show coordinate gene regulation? Yes, the same response element may be found in related genes.
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Changes in Chromatin structure and eukaryotic gene regulation Chromatin Structure –DNase hypersensitivity ( Histone acetylation DNA methylation
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