Question

QUESTION 12

1. For the lac operon to actively transcribe its genes, which of the following must happen?

   	a.	The absence of glucose leads to cAMP production, which binds to CAP, which then binds to the CAP site of the operon. Also, the presence of lactose leads to allolactose production, which binds to the lac repressor, preventing it from binding to the operator. RNA polymerase then binds to the promoter.
   	b.	The presence of glucose leads to cAMP production, which binds to CAP, which then binds to the CAP site of the operon. Also, the presence of lactose leads to allolactose production, which binds to the lac repressor, preventing it from binding to the operator. RNA polymerase then binds to the promoter.
   	c.	The absence of glucose leads to cAMP production, which binds to CAP, which then binds to the CAP site of the operon. Also, the absence of lactose leads to allolactose production, which binds to the lac repressor, preventing it from binding to the operator. RNA polymerase then binds to the promoter.
   	d.	The presence of glucose leads to cAMP production, which binds to CAP, which then binds to the CAP site of the operon. Also, the absence of lactose leads to allolactose production, which binds to the lac repressor, preventing it from binding to the operator. RNA polymerase then binds to the promoter.

Answer 1

Q12a) For the lac operon to actively transcribe its gene , it is required to have  absence of glucose which leads to cAMP production ,which binds to CAP ,which then binds to the CAP site of the operon .Also the presence of lactose leads to allolactose production ,which binds to the lac repressor ,preventing it from binding to the operator .RNA polymerase then binds to the promoter .

Lac operon consists of one regulatory gene or inhibitor gene ,one promoter gene ,one operator gene and three structural gene .A polycistronic gene is regulated by a common promoter and regulatory gene.Francis and Jacob proposed the model of gene regulation known as operon .In E .Coli , breakdown of lactose requires three enzyme. These enzymes are synthesized together in a cordinated manner by functional unit of DNA i.e, lac operon.Since the addition of lactose itself stimulates the production of required enzymes ,thus it is called as inducible system