In an E. coli strain the i gene gets mutated and its product can not bind the inducer molecule. If the growth medium is provided with lactose, what will be the outcome?
Answer: (C) z, y, a genes will not be translated. Answer: (C) z, y, a genes will not be translated.
- A.Only z gene will get transcribed
- B.z, y, a genes will be transcribed
- C.z, y, a genes will not be translated✓
- D.RNA polymerase will bind the promoter region
Correct Answer
(C) z, y, a genes will not be translated
Solution & Explanation
Answer: (C) z, y, a genes will not be translated. The i gene codes for the repressor; if the mutated repressor cannot bind the inducer (lactose/allolactose), it remains active and stays bound to the operator, so RNA polymerase cannot transcribe the operon — hence the z, y, a structural genes are not transcribed and consequently not translated. NCERT Ch 5, p.101, lines 011-016: "The repressor protein binds to the operator region of the operon and prevents RNA polymerase from transcribing the operon. In the presence of an inducer, such as lactose or allolactose, the repressor is inactivated by interaction with the inducer."