Question

Choose the correct answer from the alternatives given :
Inducible operon system usually occurs in (i) ............pathways. Nutrient molecules serve as (ii)............ to stimulate the production of the enzymes necessary for their breakdown. Genes for inducible operon are usually switched (iii)............ and the repressor is synthesised in an (iv)............... form.

• A. (i) anabolic (ii) corepressor (iii) on (iv) inactive
• B. (i) anabolic (ii) inducer (iii) off (iv) active
• C. (i) catabolic (ii) inducer (iii) off (iv) active
• D. (i) catabolic (ii) corepressor (iii) on, (iv) inactive

Answer 1

Answer: (C)

(i) catabolic (ii) inducer (iii) off (iv) active

Operon is of two types, inducible and repressor. Inducible operon system is one in which genes for inducible operon remains switched off but becomes active in the presence of an inducer. It usually occurs in catabolic pathways. In this, nutrient molecules serve as an inducer to stimulate the production of the enzyme necessary for their breakdown. For example, in lac operon, allolactose acts an inducer. In this, the repressor is synthesized always in an active form.

Thus, the correct answer is '(i) catabolic, (ii) inducer, (iii) off, (iv) active.'