Question

In E. Coli, the gene laci codes the lac operon repressor. Which of the following statements is true about an E.coli strain, which is laci-, that is null mutant for laci.

a. There would be no lac operon repression, thus lacA, lacZ and lacY genes would be constitutively expressed regardless of the presence of lactose.
b. There would be no lac operon repression, thus lacA, lacZ and lacY genes would be expressed in the presence of lactose.
c. There would be no lac operon repression, thus lacA, lacZ and lacY genes would be constitutively expressed regardless of the presence of glucose.
d. There would be no lac operon repression, thus lacA, lacZ and lacY genes would be expressed in the presence of allolactose.

Answer 1

In an E. coli strain that is lacI- (null mutant for the lacI gene), there would be no repression of the lac operon, leading to constitutive expression of the lacA, lacZ, and lacY genes regardless of lactose presence.

a is correct

Step-by-step explanation:

In E. Coli, the lacI gene produces a repressor that regulates the expression of the lac operon, which includes the genes lacA, lacZ, and lacY. These genes are necessary for the metabolism of lactose. When the lacI gene has a null mutation, indicated by lacI-, it results in the inability to produce the functional repressor protein. Consequently, the lac operon would not be repressed

The correct statement about an E. coli strain that is lacI- would be:

a. There would be no lac operon repression, thus lacA, lacZ and lacY genes would be constitutively expressed regardless of the presence of lactose.

This is because without the repressor, RNA polymerase can freely transcribe the operon, leading to the continuous production of the enzymes required to metabolize lactose.

Answer 2

The correct answer will be option-A.

Step-by-step explanation:

Lac operon is a set of genes arranged sequentially for lactose metabolism in E.coli. The lac operon gets activated in the presence of lactose as the lac operon consists of three enzyme coding genes called lacZ which codes for the β-galactosidase enzyme, lacY which codes for lactose permease, lacA which codes for acetyltransferase along with a regulatory gene called lacI which codes for repressor proteins.

The repressor proteins bind to the operator and control the transcription. When it binds to operator its huts off the transcription. If a mutation occurs in the laci gene then the protein will lose the machinery which will turn off the activity of enzymes and will lead to the constitutive expression of the genes irrespective of the inducer present or not.

Thus, option-A is the correct answer.