Which of the following statements about lac-operon is correct?
- Galactose can act as an inducer of lac operon
- Gene i is constitutively expressed
- Lactose activates repressor to bind to the operator
- Genes i, z, y and a share single common promoter
Answer
(2) Gene i is constitutively expressed
Solution
(1) Incorrect: As per NCERT, lactose (not galactose) is the inducer of the lac operon.
(2) Correct: The repressor of the operon is synthesised (all the time – constitutively) from the i gene.
(3) Incorrect: Lactose (inducer) binds the repressor and inactivates it, so the repressor cannot bind the operator.
(4) Incorrect: The structural genes z, y and a are transcribed from a common promoter; the regulatory gene i has its own promoter.
Answer: (2)