MCAT Question of the Day

  • Q:

    The preferred food source for E. coli is glucose, but in the absence of glucose, E. coli can metabolize other sugar sources, like tremalose. The tremalose operon is regulated by a repressor protein which ONLY binds to the operator in the absence of tremalose. Moreover, the operon is also regulated by an activator which ONLY binds to the promoter (where RNA polymerase binds) in the absence of glucose. Binding of this activator is needed for any expression of tremalose operon genes. Which of the following correctly describes the conditions under which the tremalose operon will be expressed?



    In the presence of BOTH glucose and tremalose


    In the absence of BOTH glucose and tremalose


    In the presence of glucose and the absence of tremalose


    In the absence of glucose and the presence of tremalose



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