Final answer:
When E. coli transitions from glucose to lactose metabolism, there is an increase in detectable lactose permease due to derepression of the lac operon in the absence of glucose. Phosphorylated proteins and cAMP-CAP complex play pivotal roles in this transition, regulating the uptake and metabolism of lactose only when it is needed.
Step-by-step explanation:
Lactose Metabolism Transition in E. Coli
When E. coli cells transition from glucose to lactose metabolism, there is an increase in the amount of detectable lactose permease. Lactose permease is an enzyme that facilitates the uptake of lactose into the bacterial cell. However, if glucose is present, its utilization prevents the lac operon from being expressed, which means lactose permease and other necessary enzymes are not produced in large quantities. As glucose levels drop, the suppression of the lac operon is lifted, and E. coli can then increase the production of lactose metabolizing enzymes to utilize lactose. The correct interaction at the lac operon when lactose is not being utilized involves the binding of the repressor protein to the operator region, preventing transcription. This is depicted in classic experiments and figures relating to the lac operon regulation.
The lac operon is further regulated through inducer exclusion and the action of catabolite activator protein (CAP). When glucose is present, phosphorylated EIIA Glc inhibits lactose permease from importing lactose. In the absence of glucose, cyclic AMP (cAMP) accumulates in the cell, which binds to CAP, allowing the initiation of transcription for lactose utilization. This delicate regulation ensures E. coli prioritizes glucose consumption over lactose and only utilizes lactose when necessary.