Question

Which enzyme/s will be produced in a cell in which there is a nonsense mutation in the lac $y$ gene?

• A. $\beta$-galactosidase
• B. Lactose permease
• C. Transacetylase
• D. Lactose permease and transacetylase

Answer 1

Answer: (A)

$\beta$-galactosidase

Nonsense mutation is a type of mutation in which sense codon is changed to a chain-terminating codon. The lac genes encoding enzymes are lac Z, lac Y, and lac A. Transcription of lac Z gene occurs before transcription of lac Y & lac A. A nonsense mutation in the lac Y gene will produce nonfunctional permease. A stop codon will be introduced in the sequence after lac Z gene. Since only $\beta$ galactosidase enzyme is produced and permease and transacetylase enzymes are not produced, lactose is not transported into the cell.

Thus, the correct answer is option A.