Question

In the Lac Operon, which molecule acts as an inducer?

• A. Glucose
• B. Lactose
• C. Galactose
• D. Maltose

Hint:

Lac operon → Lactose (allolactose) = Inducer → Turns ON gene expression.

Answer 1

The Correct Option is B

Concept: The lac operon is a classic model of gene regulation in prokaryotes, controlling the metabolism of lactose in E. coli.
Step 1: Understanding the inducer.
An inducer is a molecule that initiates gene expression by inactivating the repressor protein.
Step 2: Role of lactose.
Lactose (specifically its isomer allolactose) binds to the repressor protein, causing it to detach from the operator site.
Step 3: Effect on gene expression.
Once the repressor is removed, RNA polymerase can transcribe genes required for lactose metabolism.
Step 4: Eliminating other options.

• Glucose: Represses lac operon (catabolite repression)
• Galactose and Maltose: Not involved in lac operon induction

Step 5: Conclusion.
Thus, lactose acts as the inducer in the lac operon system.