Question

Which of the following is required as inducer for the expression of Lac operon?

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

Answer 1

The correct option is B

Lactose

The correct option is : B

Explanation of the correct option:

1. The lac z, lac y and lac a genes in lac operon are the structural genes that code for beta-galactosidase which converts lactose into glucose and galactose.
2. In lac operon, Lactose acts as an inducer for the synthesis of protein.
3. Lactose goes and binds with the repressor protein, causing an allosteric shift.
4. This altered repressor cannot bind to the operator, thereby making the promoter region accessible.
5. As the promoter region gets activated, the RNA polymerase enzyme initiates the transcription of the lac operon.
6. Thus, lactose is required for the expression of the lac operon.

Explanation of the incorrect option:

Option A:

1. In the presence of beta-galactosidase, lactose gets converted into glucose and galactose.
2. Hence, lactose is an inducer in lac operon whereas galactose is a product.

Option C:

Galactose is the end product of lac operon, which is formed by metabolizing lactose with the help of beta-galactosidase enzyme.

Option D:

Glucose is also an end product of lac operon, it represses the lac operon after its production.

Final answer: Lactose is required as inducer for the expression of Lac operon.