Question

E. coli was inoculated into the following 3 flasks: Flask A: Glucose + minimal salts broth Flask B: Glucose + Lactose + minimal salts broth Flask C: Lactose + minimal salts broth Which flask would have the enzyme -galactosidase, an enzyme translated from the lac operon? Explain your answer.

Answer 1

The lac operon or lactose operon is an operon required for the transport and metabolism of lactose in Escherichia coli. The lac operon allows for the effective digestion of lactose through the activity of beta-galactosidase. It is an example of gene regulation in prokaryotic organisms. This operon consists of 3 genes needed to produce proteins required for breaking down lactose as the sugar source on the bacterial cell. Specifically, lacZ codes for gene translation for enzyme beta-galactosidase that breaks down lactose into glucose and galactose. Now, the lac operon is operational only when a high level of lactose is present and glucose is absent. In the absence of lactose, the lac repressor binds to the operator and prevents transcription. In the presence of lactose, the transcription is active with the help of an inducer(allolactose) that binds the repressor to allow transcription. Flask A contains only glucose, which inhibits transcription by lac operon and Flask B also contains glucose with lactose, which allows the minimalistic activity of lac operon for some lactose to be formed after glucose is depleted(this phenomenon is called leaky expression). Flask C contains only lactose, so E.coli can easily activate lac operon and beta-galactosidase is produced by the lacZ gene as the translational product. Therefore, we can find the enzyme beta-galactosidase in Flask C.