Question

Identify the correct labellings for Q, R, S and T for the lac operon in E.coli as given below :


Choose the correct option from the given table :

$\begin{array}{ccccc}& \text{Q}& \text{R}& \text{S}& \text{S}\\ \text{(A)}& \text{Structural gene}& \text{Operator}& \beta \text{-Galactosidase}& \text{Repressor}\\ \text{(B)}& \text{Regulatory gene}& \text{Prometer}& \text{Transacetylase}& \text{Repressor protein}\\ \text{(C)}& \text{Structural gene}& \text{Operator}& \text{Permease}& \text{Repressor protein}\\ \text{(D)}& \text{Regulatory gene}& \text{Promoter}& \beta \text{-Galactosidase}& \text{Repressor}\end{array}$

Answer 1

Answer (B)

The Lactose operon gene in E.coli is a polycistronic gene, A is a repressor that binds to the inducer region in absence of Lactose, in presence of Lactose the inducer protein binds to the repressor.

Q- is Regulatory gene codes for the repressor protein of the operon, which is synthesized in constant amounts.

R-This is permease, a transporter protein that transports Lactose from the medium into the cell

S- is the Promoter, which is a DNA segment that serves to initiate transcription of a gene by providing the binding site for RNA polymerase. They are present upstream near the transcription start sites of genes.

T- The repressor has an affinity for the operator gene. It binds to the operator and prevents the RNA polymerase from transcribing the structural genes. When repressor binds to the operator, the operon is switched off and transcription is stopped.

The labelled parts Q, R, S and T in the given lac operon are as follows :