The lac repressor has been mutated so that its binding site for the operator has been altered to the extent that it is unable to bind to the operator.What is the likely effect of this mutation on the lac operon?
A) The repressor will be unable to bind to the operator; the operon will bind RNA polymerase and it will thus be turned on.
B) The repressor will bind to the operator despite the mutation, and will suppress transcription of the operon in the presence and absence of lactose.
C) The lac operon will be protected by the altered repressor.
D) The repressor will be unable to bind to the operator; therefore, the ability of RNA polymerase to bind there will be severely hampered.

Question

Quizplus · Accepted Answer

The lac repressor is a negative regulator of the lac operon. It binds to the operator region, blocking the progression of RNA polymerase and preventing transcription of the operon. If the binding site of the repressor for the operator region is mutated such that it cannot bind to the operator, it will be unable to block RNA polymerase from progressing, and the operon will be transcribed as a result. Thus, the lac operon will be turned on.

The Lac Repressor Has Been Mutated So That Its Binding