Question

Mention the components of bacterial transcriptional switches. The Lac operon is regulated by both activator CAP and Lac repressor. A scientist introduces a mutation in the gene encoding the activator CAP, making this allosteric protein insensitive to glucose levels. What outcomes do you expect if you culture the mutated bacteria in a culture medium with glucose and lactose. Give your explanation based on the mechanism of the Lac operon.

Answer 1

The bacterial transcription unit consists of - a regulator site, a promoter site, an operator site and the structural components of the unit which has gene encoding for protiens.

The catabolite regulating protien (CAP) regulates the amount of glucose in the cell of the bacteria. If low amount is present it usually becomes activated by detecting the levels of cAMP in the cell which is a hunger signal molecule.

The preferred molecule for energy production is glucodg and lactose is only used when glucose level is low. When glucose level is low, cyclic AMP is high and hence it binds to CAP and then this whole complex binds to the CAP site and the transcription occurs. Hence lactose is now used since the glucose level was low. Hence the CAP usualy is a check for the determination of which molecule to be used up by the bacteria.

So when the mutation occur in the CAP , there is no longer differentiation of amount of glucose and lactose present and lactose now becomes the preferred substrate inspite of when the glucose level is adequate.