High glucose levels decrease activity of the galactoside permease transporter. when lactose and glucose levels are high outside the cell, what will be the effect on lactose transport

There will be a decrease in lactose transport due to the presence of high glucose levels.

Further explanation:

The lac operon has genes for lactose metabolism in bacteria. The prime condition for the proper functioning of the lac operon is the high levels of lactose and absence or less amount of glucose in the bacterial cell.

There are three genes present in the lac operon to metabolize lactose. It also contains catabolite activator protein (CAP) and lac repressor which are responsible for sensing levels of glucose and lactose, respectively. The lac repressor usually inhibits the operon but acts opposite in the presence of lactose. The CAP protein activates the operon only in the absence of glucose.

The E. coli or bacteria utilize glucose and lactose as energy source. The breakdown of glucose involves fewer steps and comparatively less energy, therefore glucose is the prime source of energy. In glucose absence, the bacteria use lactose for energy.

When lactose is abundant, the enzyme galactosidase permease helps in the transport of lactose inside the cell and the operon functions for the transcription of lactose. A low glucose level also activates lac operon as during this time high levels of cAMP are present which binds to CAP and the dimer helps in the proper binding of RNA polymerase to the lac promoter. This, in turn, activates the lac operon.

In the presence of glucose, cAMP cannot be activated due to the inhibition of adenylyl cyclase and also galactosidase permease is inhibited which resists the transport of lactose inside the cell. As a result, lactose transport is reduced and also glucose is utilized because of its abundance.  

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Answer details:

Grade: High School

Subject: Biology

Chapter: Lac Operon

Keywords:

Lac operon, lactose, galactosidase permease, glucose, cAMP, adenylyl cyclase, transcription, CAP, lac repressor.

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