Which of the following cannot act as inducer ?

Options

A. Glucose
B. Lactose
C. Galactose
D. Both (a) and (c)

Answer

To solve the question "Which of the following cannot act as inducer?", we will analyze each option provided in the context of the lac operon and the role of inducers.

### Step-by-Step Solution:

1. **Understanding Inducers**:
- Inducers are molecules that initiate the expression of genes. In the context of the lac operon, an inducer binds to a repressor protein, causing it to change shape and detach from the operator region of the operon, allowing transcription to occur.

2. **Analyzing the Options**:
- **Option A: Glucose**:
- Glucose is a primary energy source for bacteria and does not induce the lac operon. In fact, the presence of glucose inhibits the expression of the lac operon through a mechanism known as catabolite repression.
- **Option B: Lactose**:
- Lactose is the classic inducer for the lac operon. When lactose is present, it binds to the repressor protein, allowing the transcription of genes necessary for lactose metabolism.
- **Option C: Galactose**:
- Galactose is a sugar that can be derived from lactose but does not act as an inducer for the lac operon. It does not bind to the repressor in the same way that lactose does.
- **Option D: Both A and C**:
- Since both glucose (A) and galactose (C) do not act as inducers for the lac operon, this option suggests that both cannot act as inducers.

3. **Conclusion**:
- Based on the analysis, the correct answer is **Option D: Both A and C cannot act as inducers**.

### Final Answer:
**D. Both A and C cannot act as inducer.**

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