Cellular and Molecular Biology

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Functioning of the lac Operon


In the following passage, highlight the word or phrase that is INCORRECT.

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In E. coli, the expression of genes of the lac operon is partly under the control of a negative inducible system. Such a system involves a repressor molecule that inhibits gene expression except in the presence of an inducer substance that interferes with the action of the repressor. In lac control, the repressor is a protein and the inducer is an isomer of the disaccharide lactose, called allolactose. The gene for the repressor protein is expressed constitutively, meaning at all times. The repressor binds to the operon's promoter, preventing RNA polymerase from transcribing the lac genes. When allolactose is present in the cell, it binds to repressor molecules, causing them to alter their shapes so that they cannot effectively prevent transcription.