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

Options

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

Answer

To answer the question regarding which of the following is required as an inducer for the expression of the Lac operon, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Lac Operon**: The Lac operon is a cluster of genes in bacteria that is responsible for the metabolism of lactose. It consists of three structural genes (Z, Y, and A), a promoter, an operator, and a regulatory gene.

2. **Role of the Inducer**: The inducer is a molecule that initiates the expression of the operon. In the case of the Lac operon, the presence of an inducer is necessary to prevent the repressor protein from binding to the operator, which would block transcription.

3. **Identifying the Inducer**: The primary inducer for the Lac operon is lactose. When lactose is present, it binds to the repressor protein, causing a conformational change that prevents the repressor from binding to the operator. This allows RNA polymerase to bind to the promoter and initiate transcription of the structural genes.

4. **Considering Other Options**: The options provided include:
- Lactose
- Lactose and galactose
- Glucose and galactose

Among these, only lactose is specifically known to act as the inducer for the Lac operon. Galactose is a product of lactose breakdown, and glucose does not induce the Lac operon; in fact, high levels of glucose inhibit the operon.

5. **Conclusion**: Therefore, the correct answer to the question is **Lactose**.