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What is "lac operon"?

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Quick Answer

The lac operon is a set of genes found in certain bacteria that controls the conversion of lactose into the sugars galactose and glucose. The lac operon is made up of a promoter, an inhibitor, an operator and three genes called lac Z, lac Y and lac A.

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What is "lac operon"?
Credit: Saroj Wegmi CC-BY-2.0

Full Answer

The lac Z gene encodes for the enzyme beta-galactosidase, which converts lactose into galactose and glucose. The lac Y gene corresponds to the enzyme beta-galactoside permease, which moves lactose into cells so that beta-galactosidase can convert it into other sugars for energy. This enzyme is also called lactose permease. Finally, the lac A gene encodes the enzyme beta-galactoside transacetylase, which transfers an acetyl group onto lactose. Unlike the lac Z and lac Y genes, the lac A gene is not required for lactose metabolism in bacteria.

Several mutations in the various lac operon genes have been identified. A mutation in the promoter region completely shuts down lactose metabolism since RNA polymerase is unable to bind to the promoter and begin transcription of the necessary enzymes. Mutations in the lac Z gene prevent conversion of lactose into glucose and galactose, whereas mutations in the lac Y gene prevent entry of lactose into the cell.

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