(i) Arrangement of different genes in bacteria are
(a) Structural gene (b) Operator gene
© Promoter gene (d) Inhibitory/regulatory gene
An operator gene lies adjacent to the structural gene. Promoter gene lies on its other side. On the other side of promoter gene, lies regulatory/inhibitory gene. (2)
(ii) Role of lactose in lac operon are as follow:
(a) It is the substrate for the enzyme p-galactosidase.
(b) It functions as the inducer and regulates the switching on and off of the operon.
© When lactose is present, it combines with the repressor protein, which otherwise has high affinity for the operator.
(d) It inactivates the repressor from binding to the operator and hence, transcription continues, i.e. the operon is switched on.