Question

Match the component of 'lac operon' of E.coli given under column-I with their function listed in column-II. Choose the answer with the correct combination of alphabet of the two columns:

Column-I	Column-II
(A) Structural gene	(i) Binding site for a repressor protein
(B) Operator gene	(ii) Codes for a repressor protein
(C) Promoter gene	(iii) Induce lactose transport from the medium
(D) Regulator gene	(iv) Codes for protein enzyme
	(v) Binding site for RNA polymerase

• A. A - i, B - iv, C - ii, D – iii
• B. A - iv, B - ii, C - i, D - iv
• C. A - iii, B - i, C - v, D – ii
• D. A - ii, B - iii, C - iii, D - i

Answer 1

The correct option is C A - iii, B - i, C - v, D – ii

Structural genes: These genes synthesize mRNAs, which in turn synthesize polypeptides or enzyme with the help of ribosomes. They helps in entry of lactose in the cell from outside. (A - iii)

Operator gene: It lies adjacent to the structural genes and directly controls mRNA synthesis over the structural genes. It is the binding site for repressor protein. (B - i)

Promoter gene: This gene is the site for initial binding of RNA polymerase. When the operator gene is turned on, the enzyme RNA polymerase moves over it and reaches the structural genes to perform transcription. (C - v)

Regulator gene: It produces a repressor that binds to the operator gene and stops the working of the operator gene. (D - ii)