Question

In his studies of alcoholic fermentation by yeast, Louis Pasteur noted that the sudden addition of oxygen (O2) to a previously anaerobic culture of fermenting grape juice resulted in a dramatic decrease in the rate of glucose consumption. This "Pasteur effect" can be counteracted by the addition of 2,4-dinitrophenol (DNP), un uncoupler of oxidative phosphorylation.

(a) Why would the yeast cells consume less glucose in the presence of oxygen? can you estimate how much less glucose they would use?

(b) Why would DNP counteract or prevent the Pasteur effect?

Answer 1

A

The amount of glucose required to produce a certain quantity of ATP id different under aerobic and anaerobic conditions. Under anaerobic conditions, yeast can make only 2 mols of ATP from 1 mol of glucose. However, under aerobic conditions, it can make 32 mols ATP from 1 mol of glucose. Hence, in the presence of oxygen, yeast begins to consume less amount of glucose.

Under anaerobic conditions, yeast needs to use 15-16 times more glucose as compared to aerobic conditions - to produce the same quantity of ATP

B

DNP is responsible for blocking the production of ATP from glucose, under aerobic conditions. Hence , even though oxygen is present, yeast needs to use more glucose molecules to produce the same quantity of ATP.