Match List-I with List-II:
| List-I | List-II |
|---|---|
| Genes | Proteins – codes for lac operon |
| (A) ‘i’ | (I) permease |
| (B) ‘a’ | (II) β-galactosidase |
| (C) ‘y’ | (III) transacetylase |
| (D) ‘z’ | (IV) repressor |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A)-(IV), (B) - (III), (C) - (I), (D) - (II)
(A) ‘i’ — this matches (IV) repressor. The i gene is the regulator gene (‘i’ from inhibitor). Its repressor protein binds the operator and switches the operon off when lactose is absent.
(B) ‘a’ — this matches (III) transacetylase. The a gene is the third structural gene of the operon. It codes for transacetylase.
(C) ‘y’ — this matches (I) permease. Permease makes the cell permeable to β-galactosides, so lactose can enter the bacterium.
(D) ‘z’ — this matches (II) β-galactosidase. This enzyme breaks lactose into galactose and glucose, which the cell can use.
Note: A similar question was also asked in CUET (UG) 2025 on 29-05-2025 (Slot 1), and in CUET (UG) 2022 on 30-08-2022 (Slot 2).
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), which is primarily responsible for the hydrolysis of the disaccharide, lactose into its monomeric units, galactose and glucose. The y gene codes for permease, which increases permeability of the cell to β-galactosides. The a gene encodes a transacetylase.”