Which of the following statements pertaining to regulation of gene ex…

The correct answer is Option (4) → C and D only

The lac operon of E. coli has one regulatory gene, the i gene, and three structural genes z, y and a.

(A) ‘i’ gene codes for the inducer of the lac operon. — Incorrect. The i gene codes for the repressor. The letter i comes from “inhibitor” and does not stand for inducer. The inducer is lactose, or allolactose, and it is not made by this gene.

(B) ‘z’ gene codes for permease, and ‘y’ gene codes for beta-galactosidase. — Incorrect. The roles are reversed for the two genes. The z gene codes for beta-galactosidase, the enzyme that breaks lactose into galactose and glucose. The y gene codes for permease, which lets lactose enter the cell.

(C) The repressor protein binds to the operator region of the operon. — Correct. The bound repressor blocks the way of RNA polymerase, so the structural genes are not transcribed.

(D) Lac operon is an example of inducible operon. — Correct. The operon is switched on by an inducer. When lactose is present, it binds to the repressor and makes it inactive, and transcription proceeds. So the operon is inducible.

NCERT Extract:
The Lac Operon – “The lac operon consists of one regulatory gene (the i gene – here the term i does not refer to inducer, rather it is derived from the word inhibitor) and three structural genes (z, y, and a). The i gene codes for the repressor of the lac operon. The z gene codes for beta-galactosidase (β-gal), … The y gene codes for permease, which increases permeability of the cell to β-galactosides.”
“The repressor of the operon is synthesised (all-the-time – constitutively) from the i gene. The repressor protein binds to the operator region of the operon and prevents RNA polymerase from transcribing the operon. In the presence of an inducer, such as lactose or allolactose, the repressor is inactivated by interaction with the inducer. This allows RNA polymerase access to the promoter and transcription proceeds (Figure 5.14).”