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Postby Edher » Wed Feb 16, 2005 7:13 am

I have a question regarding why FADH2 is less effective than NADH to produce energy. This is what is written in the book,

FADH2 transfers its electrons to cytochrome II (at a lower energy level than NADH). This means that the electron transport chain provides about 1/3 less energy for ATP synthesis using FADH2.

Why doesn't this mean that there would be more energy given off when the electrons attach to 02? After all, the overall amount of energy would be the same. There would just be more of a violent emission of energy. (More energy would be given off in a shorter time) Then again, that's the whole point of the Electron Transport Chain. To divide the energy into a series of steps. But if that's so, why would there be FADH2 to begin with. Wouldn't all NADH be more efficient?

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Postby Jelanen » Fri Mar 04, 2005 3:07 am

Think of it like this: Every time the electron is handed to another cytochrome, it pumps H+ across a membrane to create a gradient. NADH sticks the electron in higher up the chain than FADH2 does so the NADH electron pumps more protons since it is passed between more cytochromes than the FADH2 electrons. Since every proton pumped across is an ADP-->ATP reaction, the more protons an electron can pump, the more energy you get from that electron. FADH2 is around because it has roles in other areas like synthesis, so by being a little more multifunctional than NADH it sacrifices some in the electron transport role.

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