3. Oxidative phosphorylation (50 pts) A) In his studies of alcoholic fermentatio

Question

3. Oxidative phosphorylation (50 pts) A) 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), an uncoupler of oxidative phosphorylation. (i) Why woulo the yeast cells consume less glucose in the presence of oxygen? ) How much less glucose they would use? (ii) Why would DNP counteract or prevent the Pasteur effect? Which molecule has greater redox potential: NADH or FADH2? How is this difference in potential reflected in the flow of electrons into/through/out of the electron transport chain? What conditions/products/reagents specifically regulate oxidative phosphorylation (electron transport and chemiosmosis)? Explain. At which two steps of oxidative phosphorylation are protons "pumped" across the inner mitochondrial membrane? By what mechanism are other protons "translocated" across this membrane? B) C) D)

Explanation / Answer

Answer - A

(1) Yeast cells can produce energy in both ways aerobically as well as anerobically.

In case of Anaerobic condition (absence of oxygen):

1 glucose molecule produce 2 ATP

But, in Aerobic condition (presence of oxygen):

1glucose molecule produce 36 ATP. Here the ATP act as a inhibitor of glucose breakdown which results into the low consumption of glucose by yeast cells.

(2) Aerobically, 1 glucose molecule produce = 36 ATP

Anerobically, 1glucose molecule produce = 2 ATP

Therfore, aerobically it takes 18 times less glucose for the production of 36 ATP as compare to anerobically.

(3) DNP (2,4- Dinitrophenol) function as an uncopuler of ETC from ATP production, this process lowers the ATP production . Therefore, it requires more breakdown of glucose to produce same amount fo energy.

Through this way, DNP prevent the ' Pasteur effect' from happening.

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