466n_Lectures_19-21_white

466n_Lectures_19-21_white - Gene Regulation in Prokaryotes...

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76 “Gene Regulation in Prokaryotes” Lectures 19-21
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77 III. Gene Regulation Questions How to make different proteins at different times? How to make different cells that do different things? How to make different structures from a single egg? And, how to make different species with similar sets of genes
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78 The answers to each of these questions are all founded on the concept of “genetic switches”
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79 Approaches 1. Genetics Find mutants for: a) Structural proteins that carry out functions b) Regulatory proteins that control activity of structural genes c) Regulatory elements that act in cis to control gene expression 2. Molecular Biology a) Identify and isolate genes b) Determine how they are regulated c) Determine how their protein products act.
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80 Control of Gene Expression in Bacteria and their Viruses I. Physiological Mechanisms 1. The lac operon (genetics) 2. Promoters and repressors 3. Other operons 4. Simple life cycles
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81 Physiology Cells should make the needed proteins at the right time Do not waste energy In Bacteria : often involves nutrient utilization pathway In Eukaryotes: may involve the generation of specific proteins in specific types of cells The First Model: Lactose utilization in E. coli: B -galactosidase lactose galactose + glucose (a disaccharide) H 2 0 (energy)
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82 Adaptation and Induction The presence of substrate, lactose, caused the appearance of enzyme, B -galactosidase. Was this induction an "adaptation" of the enzyme to substrate just as the bacterium "adapts" to environment? Level lactose added lactose removed 5 10 B -galactosidease ( lacZ) Permease ( lacY) l ac mRNA Induction
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83 B-galactosidase (and permease) are B-galactosidase (and permease) are inducible inducible 1. In absence of lactose 1-2 molecues/cell In presence of lactose 100,000 molecules/cell 2. Synthesized nearly simultaneously and only after lac mRNA becomes detectable. 3. Lactose (and analogs) is inducer How does a cell "KNOW" what to make? How does a cell "KNOW" what to make? [The great Lysenko vs. Monod-Jacob divide] (Instructive) (Selective) Monod, Jacob, Lwoff sought to explain induction GENETICALLY .
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84 The lac operon of E. coli .
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85 Mutants To Define Key Genetic Elements To Map Them in Relation to Each Other Types of Mutants: lac Z - defective enzyme ( B -galactosidase) lac Y - defective permease (trans) lac I - make enzyme continuously (cis) lac 0 c -make enzyme continuously Key Approach: Mutants and Merozygotes " Constitutive "
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86 Note Gene Order NOTE: All lac Genes Map Very Close Together on Chromosome Merozygotes (Partial Diploids) - To test gene functions in cis/trans
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87 Mutations that abolished enzyme activity were likely to be structural (in the enzyme). Mutations that resulted in altered inducibility (e.g.
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466n_Lectures_19-21_white - Gene Regulation in Prokaryotes...

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