Question:
Explain how the addition of lactose in the medium regulates the switching on of the lac operon in bacteria.
Explain how the addition of lactose in the medium regulates the switching on of the lac operon in bacteria.
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The lac operon is regulated by a repressor protein. Lactose acts as an inducer by inactivating the repressor, thus enabling transcription of genes for lactose metabolism.
Updated On: Jan 13, 2026
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Solution and Explanation
Step 1: The lac operon in E. coli is an inducible operon that controls the metabolism of lactose. It is normally turned off due to the binding of a repressor protein to the operator region.
Step 2: When lactose is added to the medium, a small amount of it is converted into allolactose, which acts as an inducer.
Step 3: Allolactose binds to the repressor protein, causing a conformational change that prevents the repressor from binding to the operator region. This removal of the repressor allows RNA polymerase to bind to the promoter and initiate transcription of structural genes.
Step 4: As a result, the genes lacZ, lacY, and lacA are expressed, leading to the synthesis of enzymes that help in lactose uptake and metabolism.
Step 2: When lactose is added to the medium, a small amount of it is converted into allolactose, which acts as an inducer.
Step 3: Allolactose binds to the repressor protein, causing a conformational change that prevents the repressor from binding to the operator region. This removal of the repressor allows RNA polymerase to bind to the promoter and initiate transcription of structural genes.
Step 4: As a result, the genes lacZ, lacY, and lacA are expressed, leading to the synthesis of enzymes that help in lactose uptake and metabolism.
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