Question

The following table describes different situations where different carbohydrates are available to the bacterial cell.  Using your knowledge of the gene regulation of carbohydrate utilisation genes (such as the Lac operon and now the arabinose operon), determine whether transcription will occur when the listed carbohydrates are present or absent.

Carbohydrate 1	Carbohydrate 2	Carbohydrate 3	Transcription or No transcription at the arabinose inducible promoter (AraP)
Glucose present	Lactose present	Arabinose present
Glucose present	Lactose absent	Arabinose present
Glucose absent	Lactose present	Arabinose present
Glucose absent	Lactose present	Arabinose absent

Answer 1

In the first two cases where Glucose is present, transcription at the Arap will be absent. Glucose is the most preferred source for carbon uptake by many bacterias.

In the third case where glucose is absent and Arabinose is present, we can say that Transcription at Arap will take place. As arabinose operon works in the presence of arabinose and in the absence of glucose.

In the fourth case, where both glucose and arabinose are absent, there will be no transcription at Arap.