NEETZoologyMolecular Basis of Inheritance
A researcher isolates an E. coli strain with a normal i gene, promoter, and operator, but with a nonsense mutation in the y gene that renders its product completely non-functional. If this strain is transferred from a lactose-free medium to a lactose-rich medium, what will be the primary outcome regarding the lac operon?
Options
- AThe operon will be fully induced because lactose is present in the surrounding medium.
- BThe repressor will bind to lactose outside the cell, allowing transcription to proceed.
- CThe z gene will be transcribed and translated normally, but permease will not be formed.
- DThe operon will fail to be induced because lactose cannot efficiently enter the cell.
Correct answer
D. The operon will fail to be induced because lactose cannot efficiently enter the cell.
Step-by-step solution
The lac operon consists of three structural genes: z , y , and a . The y gene codes for permease, which increases the permeability of the cell to -galactosides (lactose). For the operon to be induced, lactose must first enter the cell to bind and inactivate the repressor protein. This entry requires a functional permease enzyme. Since the mutant strain has a non-functional y gene, it cannot produce functional permease. Consequently, lactose from the medium cannot efficiently enter the cell to act as an inducer. The