Question

How does lactose get into an E. Coli cell if the lac operon is turned “off” and so the cell isn't synthesizing lactose permease?

Answer 1

Hint: Lactose is a type of sugar that can be found in milk. Lactase is an enzyme that our bodies use to break down sugar so that it can be absorbed. People with inherited diseases, on the other hand, produce insufficient lactase. It's made in the intestine. Even if they have low lactase levels, some people can digest milk products.

Complete answer:
E. coli bacteria can break down lactose, it is not their preferred fuel. If glucose was available, they would prefer to use it. Glucose degrades faster and with less energy than lactose. If lactose is the only sugar available, E. Coli will use it as an energy source right away.

Bacteria must express the lac operon genes, which encode key lactose uptake and metabolism enzymes, in order to utilize lactose. E. coli should only express the lac operon if the following conditions are met, in order to be as efficient as possible:
i) Lactose is widely available, but glucose is not.

There are two regulatory proteins at work:
- One of them, the lac repressor, functions as a lactose sensor.
- Catabolite activator protein (CAP), on the other hand, functions as a glucose sensor.

These proteins bind to the lac operon's DNA and regulate its transcription in response to lactose and glucose levels. Lactose enters the E coli cell in this manner.

Note: If lactose is not available, the lac repressor binds tightly to the operator, preventing RNA polymerase transcription. As a result, when lactose is present, the lac repressor loses its ability to bind DNA. It floats away from the operator, allowing the operon to be transcribed by RNA polymerase.