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Unformatted text preview: the attachment of RNA polymerase to the DNA, thus allowing transcription to occur. The Lac Operon also has Positive Control In addition to the negative control mechanism described earlier in this chapter, the lac operon is also regulated by a positive control mechanism. E. coli prefer glucose when both glucose and lactose are present. When allolactose binds to and inhibits the repressor, the genes that code for enzymes needed to digest lactose are transcribed but only at a low level. Much of the cell's energy comes from glucose instead of lactose. When the level of glucose is low, the level of cAMP increases. Cyclic AMP activates a molecule (CAP), which then binds to the lac promoter and enhances the rate of transcription....
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