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Transcript
Chapter 16 Control of Gene Expression Topics to discuss • DNA binding proteins • Prokaryotic gene regulation – negative inducible: lac operon – negative repressible: trp operon • 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 (of four) 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: negative inducible • The Tryptophan operon: negative repressible Francois Jacob and Jacques Monod 1961 • Studied lactose metabolism/operon in prokayotes J. Monod Won the Nobel Prize in 1965 Sources of prokaryotic energy • 1. Disaccharide • Lactose • 2. Monosaccharide • Glucose Sources of prokaryotic energy • Monosaccharide • Glucose • Disaccharide • Lactose 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 (assume only lactose is present) 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 “Why does the presence of glucose influence lactose Lac metabolism? To answer this question you need to understand this reaction ATP Adenylyl cyclase Cyclic AMP + catabolite activator protein Glucose may inhibit this enzyme Now put the pieces all together. How CAP and cAMP affects the promoter So….Conditions: Only lactose is present But…Conditions: Only glucose And Finally….Glucose and Lactose Summary Trypthophan Operon • 5 genes involved in the synthesis of the amino acid trypthophan Negative repressible operon 2 shapes to the mRNA When trp is high When trp is low Ribosome does not stall Ribosome stalls Changes in Chromatin structure and eukaryotic gene regulation • Histone acetylation • DNA methylation • RNA silencing Do eukaryotes show coordinate gene regulation? Yes, the same response element may be found in related genes. Also remember gene expression through RNA interference!
