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21 July, 23:43

In his studies of alcoholic fermentation by yeast, Louis Pasteur noted that the sudden addition of oxygen (O2) to the previously anaerobic culture of fermentation 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. (6 marks) (a) Why would the yeast cells consume less glucose in the presence of oxygen? (b) Why would DNP counteract or prevent the Pasteur Effect?

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  1. 22 July, 00:49
    A. 38 mol of ATP is yielded during aerobic oxidation of glucose while only 2 ATP is yielded during anaerobic oxidation of glucose. This will cause the yeast cell to need 19 times more glucose anaerobically and to need less glucose aerobically.

    (b) DNP is going to block the major step in aerobic ATP production causing the yeast cells to use about the same amount of glucose as anaerobic cells when compared to yeast cells without DNP present
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