The bacterium, e. coli prefer to consume glucose. if, however, there is no glucose present, they will utilize lactose as an energy source. which of the following is the regulatory mechanism occurring when there is no glucose, but there is lactose?
a. activators initiate gene expression
b. rna cannot bind to the promoter
c. no lactose metabolism genes are transcribed
d. rna polymerase is blocked
e. the repressor protein binds to the operator region

Option A

Explanation:

Usually, the cells first is able itself to regulate the usage of sugar type that yields highest growth rate and then consume sugar with lower growth rate and so on.  

Considering this scenario E.Coli first consumes glucose and then lactose however both the sugar will result into diauxic growth

cAMP is responsible for activating the enzyme involved in metabolism of non-glucose sugars. The CRP protein of cAMP receptor is mainly responsible for activating the non-sugar metabolism enzyme . Along with this,  cognate sugars also expresses gene

Hence, option A is correct

the answer to your question is:

c. complementary base-pairing