Question

In $lac$ operon system, $lac$ gene-$i$ codes for

• A. Promoter
• B. Inducer
• C. Repressor
• D. β-galactosidase

Answer 1

The correct option is C Repressor

The $lac$ operon
The $lac$ operon is an inducible operon system in $Escherichia$ coli that remains in a switched off condition. It gets highly activated only when the substance to be metabolised, lactose, is present in the cell.
Inducer
Inducer is a chemical which forms an inducer repressor complex. This prevents the repressor from binding to the operator gene.
Repressor
Repressor is a protein produced by the regulator gene ($lac$ $i$). It binds to the operator region and helps to switch off the operon. This is because the RNA polymerase cannot bind properly to the promoter which has overlaps with the operator region. Hence, the transcription of the downstream structural genes don’t take place.
Promoter
Promoter is a gene for initial binding of RNA polymerase for initiation of transcription.
β-galactosidase
β-galactosidase is an enzyme coded by the gene lac z which hydrolyses lactose into glucose and galactose.
Final answer
(B) Repressor