4. Bio313_2006_gene+regulation2

4. Bio313_2006_gene+regulation2 - Genetic Switches...

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Genetic Switches Mechanism which turns genes on and off in response to a variety of signals Consists of specific DNA sequences located near the transcription start site of a gene and the regulatory proteins that bind to them. Prokaryotic switches – simple repressors (negative control) and activators (positive control) Eukaryotic switches - complex
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Switching genes off and on in bacteria: the lac operon lac operon encodes proteins required to transport lactose into the cell and break it down Bacteria prefer glucose to lactose as a carbon source Changes in the media composition result in changes in co-factor concentrations: + lactose =high allolactose, which binds to lac repressor and removes it from DNA + glucose = low cyclic AMP, no cAMP binding to CAP activator results in its dissociation from the DNA
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The regulation of transcription in eukaryotic cells is complex Differs from prokaryotes in three major ways: 1. DISTANCE Gene regulatory proteins can act even when they are kilobases away from the promoters that they influence. Single promoter can be controlled by a multitude of regulatory elements. 2. TRANSCRIPTION INITIATION RNA Pol II transcribes all protein-coding genes in eukaryotes but cannot initiate transcription on its own. A set of general transcription factors (required at all promoters) must be assembled at the promoter before transcription can begin. The rate of transcription of a gene can be regulated by influencing one of the multiple assembly steps. 3. DNA PACKAGING Eukaryotic DNA is assembled into chromatin.
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Eukaryotic gene regulatory proteins control gene expression from a distance Eukaryotic gene enhancers are the sites at which gene activators bind. Can be located kilobases away from the promoter and upstream or downstream from the gene. Intensity of the blue reflects the probability that the red protein will be located at each position in space relative to the white protein Binding of 2 proteins to separate sites on the DNA can enhance their probability of interacting. How? DNA has limited flexibility; it can make a smooth turn ~1/200 nucleotides
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4. Bio313_2006_gene+regulation2 - Genetic Switches...

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