Question

Why would a bacteria cell benefit from expressing the lac operon only in the presence of lactose?Â

1. The cell benefits by limiting the energy spent on the expression of the lac operonA.

2. The cell needs the lac operon to be expressed in order to obtain energy from lactose.

3. The cell doesn’t benefit, it would be better if the lac operon were expressed all of the time.

4.The production of lac operon proteins requires energy, but their production allows more energy to be obtained if lactose is present

5.The cell needs lactose to provide energy so that expression of the lac operon can occur.


choose the correct. answer and explain why

Answer 1

Answer

2. The cell need the lac operon to be expressed in order to obtain energy from lactose.

Lac operon consists a set of genes called lacZ, lacY and lacA codes for beta-galactosidase, beta-galactoside permease and galactoside acetyltransferase. Bacteria requires energy in the form of simple carbon molecule glucose. Beta-galactosidase breaks down lactose into glucose molecules. Lac-operon gets active when there is lactose present and glucose is absent and synthesize beta-galactosidase enzymes for the degradation of lactose into glucose. But when the glucose is available then the synthesis of these enzymes is a wastage of energy. So, lac operon gets active only when it is necessary. LacI or the lac repressor expressed every time but in the absence of lactose it stops the production of enzymes. Also , catabolite activator proteins (CAP) remains inactive in the presence of glucose which is required for the synthesis of enzymes as CAP helps in binding RNA polymerase to the promoter of these genes. While lacI blocks binding of RNA polymerase to the promoter. So, the cell gets benefits by saving energy as lac operon expression is required only when lactose is present and glucose is absent.

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