Question

1. Predict the level of gene expression of the lac operon in the following situations: (WT- normal function, Mut- loss of function mutation) (please type so answer is easier to read)
   1. No lactose, WT repressor
   2. Lactose, WT repressor
   3. No lactose, Mut repressor
   4. Lactose, Mut repressor

Answer 1

A. Whenever there is no lactose in the medium, then repressor will bind to operator and prevent RNA polymerase from transcribing the Operon. In this condition, the operon will be switched off.

B. Whenever there is lactose in the medium, then lactose molecules act as inducer. They bind to repressor and degrade it. This makes operator free and therefore RNA polymerase can now transcribed the Operon. In this case, the Operon is switched on.

C. In this condition, lactose is not present but repressor is also mutated. The mutated repressor will not be able to bind to operator and therefore will not be able to inhibit the activity of RNA polymerase. In this condition, the Operon will be always switched on.

D. In this condition also the Operon will be switched on. It is because the repressor is mutated and also lactose is present in the medium. If the pressure is mutated, then there will be a constitutive expression of the Operon irrespective of the presence or absence of lactose. Constitutive means it will be always on.

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