Energy and Metabolism

ID #1669

When explaining the Complexes in the electron transport chain, you said that each Complex is at a lower energy level than the one before it. Does this simply mean that each Complex can pump fewer protons across the inner mitochondrial membrane than the preceding Complex, or is the energy level measured in some other way?

Be careful not to confuse overall energy level and the difference in energy level. Let's use some imaginary numbers as an example. Let's say Molecule "A" has an energy of 100 "units", and Molecule "B" has an energy level of 90 units. Let's also say that it takes 10 "units" of energy to move a proton across a special membrane. If electrons are passed from "A" to "B", enough energy is released (the difference between A and B) to pump a proton across the membrane. Now let's say Molecule "C" has an energy level of 75. The difference in energy level between B and C is even greater in magnitude than the difference between A and B, and C is at the lowest absolute energy level so far. But when electrons are passed from B to C, is enough energy released to move another proton across the membrane? Yes, more than enough. Molecule "C" might be at the lowest overall energy level of these three molecules, but it's the difference in energy that allows us to do work.

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