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So how do hydrogen electrons get trapped?

The last step in the reactions that moves energy into ATP is called electron transport. Electron transport is achieved by passing the electrons of hydrogen through four complexes of proteins.

Where do the electrons come from?
The electrons of hydrogen formed in the Krebs cycle are pulled off and transported by a series of proteins that are anchored in the inner membranes of mitochondria. Electrons are attracted to these proteins by the highly positive-charged iron atoms that are in the proteins. Basketball Image

Think of it as if each protein attached to the membrane were a basketball player, passing the ball (electron) to the next player, and so on. Because the electron has electric charge, there is associated force or energy. There is a gradient in electric charge as the electron moves from one protein to another. Some of the energy of these gradients gets captured in ATP (adenosine triphosphate).

Waterfall ImageAnother way that energy capture has been described is in terms of a waterfall that has several steps. At the top, the water (electrons) has the most energy, with less energy at each step toward the bottom. If a paddlewheel is placed at each step, the energy of the falling water could be stored in a battery for example (in cells, ATP is like a battery).

Oxygen is consumed in the process, because it reacts with hydrogen to form water. So, you can see that there is such a thing as metabolic water.  Animals that live in the desert, such as camels, are especially good at taking advantage of metabolic water to stay alive.

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