MBB 222 Lecture Notes - Lecture 28: Lac Operon, Lac Repressor, Operon
20 Dec 2018
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Document Summary
The lac operon: a well-studied example of both negative and positive regulation in bacteria -galactosidase is encoded by lacz on the lac operon; the lac operon also contains. Expression of the lac operon is repressed when glucose is available and is only activated at high levels when lactose is present and glucose levels are low. Think about this logically (in terms of supply and demand) to appreciate the economy of this system. Three structural genes in the operon, lacz, lacy and laca: these code for enzymes involved in lactose metabolism. These genes are normally expressed a very low levels (they are repressed) When lactose is present they are induced ~1000-fold higher expression. Higher expression still when glucose is absent. This regulation ensures that -galactosidase is only made when needed, when its substrate (lactose) is present and when its easier to utilize carbon source, glucose, is absent.
