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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 takes place?

1. The lac operon is repressed
2. All operons are induced
3. The lac operon is induced
4. E.coli cells stop dividing

Correct answer: The lac operon is induced

Solution

Lactose acts as the inducer of the lac operon, allowing transcription of genes needed to metabolize lactose. In the absence of glucose, repression is relieved and the operon is turned on.

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