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Download Ch 16 Lac Operon
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Chapter 16 Control of Gene Expression Topics to discuss • DNA binding proteins • Prokaryotic gene regulation • Eukaryotic gene regulation 6 groups of DNA-binding regulatory proteins have been identified Prokaryotic Gene Regulation • Operons • Operons provide coordinate expression A model operon Now let’s look at 2 groups of operons Negative inducible operons Negative repressible operons Negative inducible operon INDUCIBLE Turned on repressor Now let’s look at 2 specific operons • The Lactose operon • The Tryptophan operon Francois Jacob and Jacques Monod 1961 • Studied lactose metabolism in prokayotes Sources of prokaryotic energy • 1. Disaccharide • Lactose • 2. Monosaccharide • Glucose Building the lac operon Lac Operon and Proposed Arrangement with control I gene I P O Z Not technically part of the “operon” Y A Lactose Metabolism Requires Coordination of all these genes! Negative inducible operon Conditions: No glucose but lactose is present Lactose Metabolism Requires Coordination of all these genes! Lac Operon and Proposed Arrangement with control I gene I P O Z Not technically part of the “operon” Y A Overview of: Mutational Analysis of the lac operon 3-24p. Lab manua Monod and Jacob Discovery of lac operon control Try out your ability to reason through the questions. I gene P gene Z,A,Y genes O I+ P+ Z+,A+, Y+ O+ I- P- Z- or A-, or Y- Oc Is Β-galactosidase No Lactose 1 I+P+O+Z+Y+ 2 I-P+O+Z+Y+ 3 I+P-O+Z+Y+ 4 I+P+OcZ+Y+ 5 I+P+O+Z-Y-/ I-P+O+Z+Y+ 6 I+P+OcZ+Y-/ I+P+O+ZY+ 7 I+P+OcZ-Y+/ I-P+O+Z+Y- 8 ISP+O+Z+Y-/ I-P+O+Z-Y+ 9 I+P-OcZ+Y+/ I+P+O+Z-Y- - + + - Lactose + + + + + - Permease No lactose - + + - Lactose + + + + + - Now, back to glucose and the lac operon! Lac Question: what happens when both lactose and glucose are present together in the same cell? Conditions: glucose present and lactose Need to understand this reaction ATP Adenylyl cyclase Cyclic AMP + catabolite activator protein Glucose may inhibit this enzyme The promoter needs to be in an ideal conformation for RNA polymerase. How CAP and cAMP affects the promoter Trypthophan Operon Trypthophan Operon • 5 genes involved in the synthesis of the amino acid trypthophan Negative repressible operon 2 shapes to the mRNA attenuation Eukaryotic Gene Regulation Do eukaryotes show coordinate gene regulation? Yes, the same response element may be found in related genes. Changes in Chromatin structure and eukaryotic gene regulation • DNase hypersensitivity • Histone acetylation • DNA methylation For Your Information Next 4 slides Experimental tests on the repressor: • I+ cells synthesize full levels of the lac enzymes only in the presence of an inducer • I- mutations NO DNA BINDING ACTIVITY, TRANSCRIPTION OCCURS EVEN IN ABSENCE OF INDUCER! • Is mutation NO LACTOSE BINDING ACTIVITY but has DNA BINDING ACTIVITY. NO TRANSCRIPTION EVEN WITH INDUCER! • Oc mutation: constitutive activity Trans (across) acting product Oc= constitutive operator, notice how it affects transcription. Mutations to inducer binding domain of repressor Extra slides Table I. Table 2. Table 3. Allosteric affect of DNA binding protein The Lac promoter and its role in lac transcription Repressor has two binding sites. Lactose binding site DNA Operator binding site ITPG: Binds repressor but is not cleaved.