Question

Would a mutation that inactivated lac repressor and prevented it from binding to the lac operator site result in the constitutive expression of the lac operon under all conditions? Explain. What is the disadvantage to the bacterium of having a constitutive lac operon?

Short answer

Yes, a mutation in the lac repressor resulting in it not being able to bind to the operator would lead to the constitutive expression of the lac operon, as it would be permanently turned on. This is disadvantageous to the bacterium as it wastes energy and resources.

Step-by-step solution

Understanding Constitutive Expression

Constitutive expression in gene regulation means that a gene or set of genes is expressed continuously, under all environmental conditions.

Effects of Mutation

A mutation that inactivates the lac repressor and prevents it from binding to the operator site would leave the lac operon permanently open, leading to the continuous, or constitutive, production of the enzymes coded by its genes.

Implications for the Bacterium

While that might seem advantageous initially, the bacterium would be wasting energy and resources producing enzymes that break down lactose when lactose might not even be present. This is disadvantageous for the bacterium.