In the presence of both glucose and lactose,the lactose repressor is not bound to the operator and the genes of the lactose operon are expressed.

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Quizplus · Accepted Answer

In the presence of both glucose and lactose, the lactose repressor can be inactivated by allolactose (a form of lactose), allowing the genes of the lactose operon to be potentially expressed. However, the presence of glucose activates a separate regulatory mechanism that suppresses the expression of these genes by preventing the accumulation of cAMP, which is necessary for the activation of the operon by CAP (catabolite activator protein). Thus, the full expression of the lactose operon in the presence of glucose is inhibited, even if the repressor is not bound to the operator.

In the Presence of Both Glucose and Lactose,the Lactose Repressor