In case of catabolism of carbohydrates catabolic breakdown of glucose which is a simple carbohydrate prevents activation (repression) of the lac operon by lactose, so this effect was originally called catabolite repression a positive control of lac-operon. It is found in various bacteria and other micro-organisms.
In a culture medium of bacteria if we have both glucose and lactose . Suppose the concentration of lactose is more as in comparision to glucose. Then, glucose represses the activity of lactose . It will not allow the bacterial cells to uptake lactose first unless untill all the glucose molecules get metabolized or depleted.
It is also called as Glucose effect as in this case the glucose is the repressor .
Process-
Permease protein allows to pass the lactose inside the cell and the glucose by glucose transpoters. Glucose keep phosphotransferase enzyme in active condition which is present in the the bacterial cell. .(Switch off mechanism) it looses phosphate group and it block adenyl cyclase enzyme production(which produces cAMP). Transcription process is not possible due to lack of beta- galactosidase and permease .
Furthermore, when glucose levels are low the phosphorylated form of phosphotransferase accumulates and consequently activates the enzyme adenylyl cyclase, which will produce high levels of cAMP. cAMP binds to catabolite activator protein (CAP) and together they will bind to a promoter sequence on the lac operon.
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In a culture medium of bacteria if we have both glucose and lactose . Suppose the concentration of lactose is more as in comparision to glucose. Then, glucose represses the activity of lactose . It will not allow the bacterial cells to uptake lactose first unless untill all the glucose molecules get metabolized or depleted.
It is also called as Glucose effect as in this case the glucose is the repressor .
Process-
Permease protein allows to pass the lactose inside the cell and the glucose by glucose transpoters. Glucose keep phosphotransferase enzyme in active condition which is present in the the bacterial cell. .(Switch off mechanism) it looses phosphate group and it block adenyl cyclase enzyme production(which produces cAMP). Transcription process is not possible due to lack of beta- galactosidase and permease .
Furthermore, when glucose levels are low the phosphorylated form of phosphotransferase accumulates and consequently activates the enzyme adenylyl cyclase, which will produce high levels of cAMP. cAMP binds to catabolite activator protein (CAP) and together they will bind to a promoter sequence on the lac operon.
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