In lac operon, a structural gene is-
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Polycistronic
A cistron is a segment of DNA coding for one polypeptide. A structural gene that codes for several polypeptides is polycistronic (mostly in bacteria); one coding for a single polypeptide is monocistronic (mostly in eukaryotes). In the lac operon, the three structural genes z, y and a are transcribed together from one promoter.
Option (1) Monocistronic — Incorrect. Monocistronic genes are typical of eukaryotes; the lac operon is bacterial.
Option (2) Polycistronic — Correct. In the lac operon a polycistronic structural gene is regulated by a common promoter and regulatory genes.
Option (3) Initiator — Incorrect. ‘Initiator’ refers to starting (e.g. the initiator codon AUG), not to a kind of structural gene.
Option (4) Anticodon — Incorrect. An anticodon is the three-base loop of tRNA that pairs with a codon.
NCERT Extract:
The Lac Operon –
