Question

Lactose, but not glucose, is present in high concentrations in the culture medium for a wild type E. coli strain. Under these culture conditions, what proteins bind to the regulatory region of the Lac operon?

a. cAMP receptor protein (CRP)
b. lac repressor
c. RNA polymerase
d. lac repressor and RNA polymerase
e. cAMP receptor protein (CRP) and RNA polymerase

Answer 1

In the presence of lactose and absence of glucose, both the lac repressor and the cAMP receptor protein (CRP) play roles in regulating the Lac operon; the repressor releases from the DNA in the presence of lactose and CRP binds when glucose is absent to promote RNA polymerase binding and transcription.

Step-by-step explanation:

When lactose, but not glucose, is present in high concentrations in the culture medium for a wild type E. coli strain, the proteins that bind to the regulatory region of the Lac operon are the lac repressor and the cAMP receptor protein (CRP). The presence of lactose leads to its conversion into allolactose, which binds to the lac repressor, causing it to dissociate from the operator region. At the same time, when glucose is not present, the cellular concentration of cAMP rises. cAMP then binds to CRP, and this complex can bind to the lac operon promoter, facilitating the binding of RNA polymerase and the initiation of transcription of genes involved in lactose metabolism. Therefore, the correct answer is that both the lac repressor and the cAMP receptor protein (CRP) bind to the regulatory region of the Lac operon, with the repressor dissociating in the presence of lactose and CRP activating transcription in the absence of glucose.

Answer 2

e. cAMP receptor protein (CRP) and RNA polymerase.

Step-by-step explanation:

Lac operon is a type of inducible operon which can be controlled positively or negatively. A positively controlled operon is the one which is controlled through an activator while negatively controlled is the one which is controlled through a repressor. The inducer in case of lac operon is cAMP receptor protein (CRP) which forms a dimer and makes interaction in the upstream region of promoter of lac operon so as to facilitate transcription. Repressor in case of lac operon is a tetrameric protein which binds the operator region of lac operon and prevents gene expression by restricting RNA polymerase from facilitating transcription.

When lactose is present in high concentrations and glucose is in low concentration in the culture medium for a wild type E. coli strain, the control will be negative as well as positive.

If the glucose level is very low, an enzyme known as adenylyl cyclase becomes active and produces cAMP, this cAMP then forms a dimer by interacting with CRP to form a cAMP-CRP dimer which acts as an activator and binds to the upstream of lac promoter and helps RNA polymerase to initiate transcription.

Also because of high lactose concentration, lactose isomerises into allolactose which acts as an inducer and interacts with repressor to remove it from operator region. As soon as repressor is removed from the operator region, RNA polymerase starts transcription.