The wild type E. coli cells are growing in normal medium with glucose. They are transferred to a medium containing only lactose as sugar. Which of the following changes take place ?

Options

A. The lac operons is induced
B. E.coil cells stop dividing
C. The lac operon is repressed
D. All operons are induced

Answer

To solve the question regarding the changes that take place when wild-type E. coli cells are transferred from a glucose medium to a lactose medium, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Environment**:
- Initially, E. coli cells are growing in a medium with glucose, which is their preferred source of energy. In this environment, the lac operon (which is responsible for lactose metabolism) is repressed because glucose is available.

2. **Transition to Lactose Medium**:
- When the E. coli cells are transferred to a medium containing only lactose, the primary sugar source changes. This switch is crucial because it affects the expression of the lac operon.

3. **Role of the Lac Operon**:
- The lac operon consists of genes (lacZ, lacY, and lacA) that are involved in the metabolism of lactose. These genes are normally kept off (repressed) in the presence of glucose.

4. **Induction of the Lac Operon**:
- In the absence of glucose and presence of lactose, the lac operon is induced. Lactose is converted into allolactose, which acts as an inducer by binding to the repressor protein. This binding prevents the repressor from attaching to the operator region of the lac operon.

5. **Resulting Changes**:
- As a result of the repressor being inactivated, RNA polymerase can bind to the promoter and transcribe the structural genes, leading to the production of enzymes necessary for lactose metabolism.

6. **Conclusion**:
- Therefore, the correct answer to the question is that the lac operon is induced when E. coli cells are transferred to a medium containing only lactose.

### Final Answer:
- The lac operon is induced.

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