Question

The lactose repressor protein ________. a. is transcribed with the structural lac genes b. is activated by binding lactose c. is inactivated by binding lactose d. requires lactose for its transcription e. None of the choices are correct.

Answer 1

Answer:

c. is inactivated by binding lactose

Explanation:

Lactose is a sugar mostly present in milk or dairy products. It is degraded in the body by an enzyme called LACTASE. Since lactase is an enzyme (protein), it must be encoded by a structural gene (Lac gene). However, the expression of this structural gene can be inhibited by the absence of lactose.

Ideally, when lactose is present, it binds to a DNA binding protein called Lac repressor protein (inhibitor) causing the inhibitor protein to lose its shape and fall off, allowing transcription of the lac gene to occur. In other words, the presence of lactose deactivates the inhibitory function of lactose repressor protein.