Suppose that you are studying an inducible operon that contains two genes requir

Question

Suppose that you are studying an inducible operon that contains two genes required for the metabolism of compound xyz. Gene A encodes enzyme A, and gene B encodes enzyme B. When compound xyz is absent, the operon is repressed, but when compound xyz is present, the operon is induced. You have isolated four distinct mutants, numbered 1, 2, 3, and 4, which have the effects shown in the table below, where + indicates that the enzyme is synthesized and- indicates that the enzyme is not synthesized. Identify the component of the operon that is mutated in each mutant. xyz absent Enzyme A Enzyme B Enzyme A Enzyme B Component xyz present mutated Wild type Mutant 1 Mutant 2 Mutant 3 Mutant 4 gene A repressor gene B promoter Incorrect Whereas the components mutated in other mutants may also be incorrect, you have switched the components mutated in mutants 1 and 3 Therefore, if one of the enzymes is synthesized but the other is not, the gene that encodes the missing The genes in an operon are transcri d as a single mRNA enzyme must be mutated.

Explanation / Answer

In case of mutant 1, when compound xyz is present only the enzyme A is synthesized because the gene B is in mutated condition. So the enzyme B will not be synthesized here.

In case of mutant 2, there is a continuous expression of enzyme A and enzyme B whether the compound xyz is present or absent. It is the case of the mutation of repressor gene.

In case of mutant 3, when compound xyz is present only the enzyme B is synthesized because the gene A is in mutated condition. So the enzyme A will not be synthesized here.

In case of mutant 4, there is no expression of enzyme A and enzyme B whether the compound xyz is present or absent. So it is the case of mutation of promoter. Promoter helps RNA polymerase to bind upstream of a gene and transcribe it. If promoter is mutated, the RNA polymerase can not be bind with the operon. So no transcription of enzyme A and enzyme B will be occured.

Name of the mutant Component mutated Mutant 1 gene B mutant 2 repressor Mutant 3 gene A Mutant 4 promoter

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