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

Question

Match the following genes of the lac operon listed in column ‘A’ with their respective products listed in column ‘B’:
\[ \begin{array}{|c|c|} \hline \textbf{A: Gene} & \textbf{B: Products} \\ \hline \text{a. ‘i’ gene} & \text{(i) β-galactosidase} \\ \text{b. ‘z’ gene} & \text{(ii) lac permease} \\ \text{c. ‘a’ gene} & \text{(iii) repressor} \\ \text{d. ‘y’ gene} & \text{(iv) transacetylase} \\ \hline \end{array} \] Select the correct option:

Answer 1

To address this question, we need to understand the structure and function of the lac operon in E. coli, which is pivotal for lactose metabolism. The lac operon includes three structural genes:

lacZ: Encodes β-galactosidase, the enzyme responsible for breaking down lactose into glucose and galactose.
lacY: Encodes lactose permease, a protein that facilitates the entry of lactose into the cell.
lacA: Encodes transacetylase, which is less critical for lactose metabolism.

A nonsense mutation is a genetic alteration that results in a premature stop codon, leading to incomplete and usually nonfunctional protein products. Given that the mutation affects the lacY gene, the production of lactose permease is directly impacted, resulting in a nonfunctional or absent protein.

Now, considering how the operon is structured and gene expression occurs:

\beta-galactosidase (from lacZ) can still be produced normally because it is transcribed first in the operon and is unaffected by downstream mutations.
Lactose permease (from lacY) will not be correctly produced due to the nonsense mutation in the lacY gene.
Transacetylase (from lacA) typically follows lacY in the mRNA transcript. However, due to the nonsense mutation in lacY, the transcript is truncated, and transacetylase is unlikely to be produced correctly.

By this analysis, only β-galactosidase will be produced functionally in the cell because its encoding gene (lacZ) is unaffected by the nonsense mutation in lacY.

Answer: β-galactosidase

Answer 2

To address this question, we need to understand the structure and function of the lac operon in E. coli, which is pivotal for lactose metabolism. The lac operon includes three structural genes:

lacZ: Encodes β-galactosidase, the enzyme responsible for breaking down lactose into glucose and galactose.
lacY: Encodes lactose permease, a protein that facilitates the entry of lactose into the cell.
lacA: Encodes transacetylase, which is less critical for lactose metabolism.

A nonsense mutation is a genetic alteration that results in a premature stop codon, leading to incomplete and usually nonfunctional protein products. Given that the mutation affects the lacY gene, the production of lactose permease is directly impacted, resulting in a nonfunctional or absent protein.

Now, considering how the operon is structured and gene expression occurs:

\beta-galactosidase (from lacZ) can still be produced normally because it is transcribed first in the operon and is unaffected by downstream mutations.
Lactose permease (from lacY) will not be correctly produced due to the nonsense mutation in the lacY gene.
Transacetylase (from lacA) typically follows lacY in the mRNA transcript. However, due to the nonsense mutation in lacY, the transcript is truncated, and transacetylase is unlikely to be produced correctly.

By this analysis, only β-galactosidase will be produced functionally in the cell because its encoding gene (lacZ) is unaffected by the nonsense mutation in lacY.

Answer: β-galactosidase

List I		List II
A	Two or more alternative forms of a gene	I	Back cross
B	Cross of F₁progeny with homozygous recessive parent	II	Ploidy
C	Cross of F progeny with any of the parents	III	Allele
D	Number of chromosome sets in plant	IV	Test cross

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

The Correct Option is A

Solution and Explanation

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