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Chapter 16 Control of Gene Expression
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Topics to discuss DNA binding proteins Prokaryotic gene regulation –negative inducible: lac operon –negative repressible: trp operon Eukaryotic gene regulation
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6 groups of DNA-binding regulatory proteins have been identified
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Prokaryotic Gene Regulation
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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 (of four) 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: negative inducible The Tryptophan operon: negative repressible
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Francois Jacob and Jacques Monod 1961 Studied lactose metabolism/operon 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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Sources of prokaryotic energy Monosaccharide Disaccharide Glucose Lactose
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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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Lactose Metabolism Requires Coordination of all these genes!
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Negative inducible operon
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(assume only lactose is present)
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Next: let’s review just the pattern of expression when: When only lactose is present. When only glucose is present. Glucose and lactose are present in the cell
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“Why does the presence of glucose influence lactose metabolism? Lac
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To answer this question you need to understand this reaction Adenylyl cyclase Cyclic AMP ATP Glucose may inhibit this enzyme catabolite activator protein +
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Now put the pieces all together.
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How CAP and cAMP affects the promoter
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So….Conditions: Only lactose is present
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But…Conditions: Only glucose
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And Finally….Glucose and Lactose
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Summary
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Trypthophan Operon 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 When trp is high When trp is low
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Ribosome does not stall
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Ribosome stalls
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Changes in Chromatin structure and eukaryotic gene regulation Histone acetylation DNA methylation RNA silencing
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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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Also remember gene expression through RNA interference!
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