Question

11. Is the lac operon a repressible or an inducible operon? What happens in the absence of lactose? What happens in the presence of lactose? Is the trp operon a repressible or an inducible operon? What happens in the absence of tryptophan? What happens in the presence of tryptophan?

Answer 1

Lac Operon is an invisible type of Operon. It is because whenever the effector molecule is present, then the Operon is switched on. In this case the effector is also called as inducer and it is the lactose.

Whenever lactose is absent in the medium, then operator region is bound by lac repressor. This prevents RNA polymerase from transcribing the Operon and therefore the Operon is in a switched off condition.

But whenever there is lactose in the medium, then lactose molecule bind to repressor and degrade it. This make operator free and now RNA polymerase can transcribe the Operon. This leads to switching on of the Operon.

Tryptophan is a type of repressible Operon. It is because whenever the effector molecule is present in the external medium, the Operon is switched off. In this case the effector is tryptophan molecule and it is also called as repressor.

Whenever the tryptophan is not present in the medium, then the Operon is switched ON and leads to the synthesis of tryptophan.

But whenever the tryptophan is present in the medium, then tryptophan molecule acts as repressor and leads to the attenuation of second and third regions of operon there by switching the Operon off.

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