When glucose is substituted by lactose in the growth medium of the E. coli bacteria, lactose enters the cells and acts as an inducer of the lac operon. It then leads to transcription of enzymes that enable effective digestion of lactose.
Instead of lactose an unknown sugar medium is used and there is no glucose in the medium. How would the unknown sugar affect the lac operon?

Options

A. It will induce the lac operon.
B. It will have no effect on the lac operon.
C. It will enable its conversion to lactose which will then induce the lac operon.
D. It may or may not induce the lac operon depending on whether the repressor is being produced or not.

Answer

To solve the question regarding the effect of an unknown sugar on the lac operon in E. coli, we can follow these steps:

### Step 1: Understand the Role of the Lac Operon
The lac operon is a set of genes in E. coli that are responsible for the metabolism of lactose. It is activated in the presence of lactose, which acts as an inducer. When lactose is present, it binds to the repressor protein, preventing it from inhibiting the operon, thus allowing the transcription of genes needed for lactose digestion.

**Hint:** Recall that the lac operon is specifically responsive to lactose as an inducer.

### Step 2: Analyze the Unknown Sugar
The question states that an unknown sugar is used instead of lactose, and there is no glucose in the medium. Since the lac operon is specifically activated by lactose, we need to consider whether the unknown sugar can act as an inducer.

**Hint:** Consider whether the unknown sugar has a similar structure or function to lactose.

### Step 3: Determine the Effect on the Lac Operon
Since the lac operon is specifically induced by lactose, the presence of an unknown sugar that is not lactose will not activate the operon. Therefore, the lac operon will remain inactive because the necessary inducer (lactose) is absent.

**Hint:** Think about the specificity of inducers for operons in bacterial gene regulation.

### Step 4: Conclusion
Based on the analysis, the conclusion is that the unknown sugar will have no effect on the lac operon. It will not induce the operon since it does not provide the necessary signal (lactose) for activation.

**Hint:** Summarize the findings by stating that without lactose, the lac operon cannot be activated.

### Final Answer
The unknown sugar will have no effect on the lac operon.