Question

Consider what you know about the lac operon, and predict whether the repressor and the activator is active (able to bind to DNA) or inactive (unable to bind to DNA), and the level of transcription in the following scenarios. Options for transcription levels include high, medium, leaky and off. a. When lactose is present but glucose is not, the repressor is and the activator is leading to levels of transcription. and the activator is b. When lactose and glucose are absent, the repressor is leading to levels of transcription. and the activator is c. When lactose is absent and glucose is present, the repressor is leading to levels of transcription. d. When both lactose and glucose are present, the repressor is leading to and the activator is levels of transcription.

Answer 1

Operon is a gene regulating unit.

Lac (Lactose) operon is an typical example of operon and it consists of 3 structural gene , an operato
- E se a 5 @ When lactose is present but glucose is not the repressor is Inactive and the activator is Active deading to High levels of transcription to ② When lactose and glucose are absent, the repressor is - Active and the activator is Active leading to Off levels of transcription. © When lactose is absent and glucose is present, the repressor is Active and the activator is Inactive leading to off levels of transcription. @ When to the lactose and glucose are the are present, the repressor is Inactive and the activator is Inactive leading to Leaky levels of transcription. i
r and a promoter.

The product of lac operon is involved in conversion of disaccharide sugar (Lactose) into its monosachharide units i.e. glucose and galactose.

Lac operator is a region of DNA which lies between promoter and structural genes where repressor binds and inhibits/represses transcription of the lac operon.

If Lactose is not present in the medium,the lac repressor binds tightly to the operator and this act as a roadblock in the path of transcription.

If Lactose is present in the medium,allolactose binds with lac repressor which makes some conformational changes in the lac repressor so that lac repressor can't bind on the operator region ultimately allowing transcription process to occur.

When the bacteria has another sugars in the medium such as glucose then it has the preference to utilise glucose over Lactose.

Catabolite activator protein (CAP) act as glucose sensor and thus activates the transcription process .

CAP is related to cAMP ; cAMP is inversely proportional to the glucose concentration i.e. when glucose is present in the medium then cAMP conc. will be low and hence CAP willn't be active.

Hope this helps you...Thank you ?