MHE/Freeman by Sapling Leamin Genetics: A Conceptual Approach 6th Edition A gene
ID: 300399 • Letter: M
Question
MHE/Freeman by Sapling Leamin Genetics: A Conceptual Approach 6th Edition A geneticist is st repressor of the inducible operon. The geneticist isolates several constitutive mutants of this operon an inducible operon in a species of bacteria. A regulator gene producesa Where might mutations that cause the operon to be constitutively expressed occur? in the inducer gene in the repressor gene inthe coding region of the operon in the operator region of the operon in the promoter region of the operon How would the mutations cause the operon to be constitutive? A mutation in the repressor results in a conformational that alters the J binding site of the inducer such that the inducer cannot bind to the repressor Amudation i the promoter region of the repressor gene prevents transcription L of the repressor n The repressor is unable to bind to the operator because a mutation in the repressor gene results in a conformational change. A mutation in the operator region of the operon has altered the binding site of the repressor so that the repressor cannot bind to the operator A mutation in the promoter region of the operon results in a sequence change L in the promoter such that transcription always occurs. HintExplanation / Answer
Inducible operon remains in 'off' condition when there is no need of the downstream gene products (enzymes). A protein known as repressor protein binds with the operator region of the operon and inhits the transcription of downstream genes. This repressor protein can change its conformation when binds with the substrate of the downstream gene products (inducer). After conformational change, the repressor protein become loose from the operator so the transcription of downstream genes can take place. These downstream gene's end products (enzymes) play a crucial role in the metabolism of the substrate molecules.
If the repressor gene is mutated then it can't bind with the operator region of the operon. So, the RNA polymerase don't face any problem to transcribe the downstream genes. So, the operon will be constitutively active. If there is a mutation in the operator region of the operon then the repressor protein can't recognise the operator region. So, it can't bind with the operator. So, the RNA polymerase can again pass to the downstream gene very easily. These are the cases when the operon will be constitutively active.
There are two possible mutations by which is to be constitutive. They are - the repressor is unable to bind with the operator because a mutation in the repressor gene results in conformational change, a mutation in the operator region of the operon has altered the binding site of the repressor so that the repressor can not bind to the operator. In the first case the conformational change of the repressor is caused by the mutation so it can't bind with the operator. In the second case the operator region is changed due to mutation so the repressor can't recognise the operator region of the operon. The 1st and 5th options lead to the constitutively inactivity of the operon. The 2nd option is rejected as the repressor gene has no promoter region.
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