Lac operon

Lac operon - The lac operon in E Coli bacteria has a coding...

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The lac operon in E Coli bacteria has a coding region for three proteins necessary for the use of lactose as a food source. These proteins are only needed when lactose is available and the normal food source, glucose , is in short supply. Therefore, the regulatory region of the lac operon has two switches. One, the CAP binding site , is switched “on” only when glucose levels are low . Another, the Operator site, is switched “on” only when lactose is present. Both of the switches must be “on” to allow expression of the lac operon genes. The CAP binding site is next to promoter for the lac operon. When the level of glucose is low, a high level of a compound called cAMP builds up in the cell. A complex of cAMP and a protein called CAP binds to the CAP binding site, bending the DNA and allowing RNA polymerase to bind at the promoter. When the glucose level is high, there is not enough cAMP, so nothing binds at the CAP binding site. This keeps RNA polymerase from binding at the promoter, thus preventing expression of the lac operon genes. The operator site is also next to the promoter. When lactose is absent, a repressor protein will bind at the operator site and prevent RNA polymerase from binding at the promoter.
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When Lactose is present, a lactose isomer will bind to the repressor and prevent it from binding to the operator site. Thus, only when the glucose level is low
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Lac operon - The lac operon in E Coli bacteria has a coding...

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