THE MOLECULAR BASIS OF INHERITANCE
GENE MUTATION
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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The lac operon would be on all the time
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The lac operon would be off all the time
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There would be no change in the expression of the lac operon because the repressor does not affect the operon itself.
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It would depend on the presence of glucose.
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Detailed explanation-1: -a) Most mutations in the operator, the binding site for repressor, lead to lower affinity for the repressor and hence less binding. Thus these mutations allow continued transcription (and thus expression) of the lac operon even in the absence of inducer; this is referred to constitutive expression.
Detailed explanation-2: -A mutation occurring in the lac I gene causes the inability of the repressor to bind with the operator. If the repressor does not bind the operator, RNA polymerase will move to the transcription site and do transcription even if lactose is absent.
Detailed explanation-3: -It is due to the lack of binding of repressor to the operator region. The mutation changes the sequence of the lac operator, which will then accept the repressor molecules. As a result, a cell will continuously produce the beta-galactosidase enzyme to utilize lactose in the absence of lactose.
Detailed explanation-4: -What would happen if the operator sequence of the lac operon contained a mutation that prevented the repressor protein from binding the operator? In the presence of lactose, the lac operon will not be transcribed. In the absence of lactose, the lac operon will be transcribed.