Energy and Metabolism

ID #1670

Which comes first, the ETC or Ox. phosphorylation? I thought Ox.Phosphorlyation was a description of the reactions occurring in the ETC.

We should make it very clear right away that oxidative phosphorylation is NOT something that happens in the ETC. Don't let the overall complexity of respiration confuse you -- the ETC is fairly simple in its function. It's just the sequential movement of electrons from a reduced cofactor (NADH or FADH2) to oxygen. Energy is released during this transfer of electrons, and that energy is harnessed to do some work -- pumping protons from the mitochondrial matrix to the intermembrane space. No ATP is actually synthesized during the process of electron transport, which ends with the production of water and an electrochemical gradient across the inner mitochondrial membrane. AFTER the ETC, or perhaps more accurately because of it, oxidative phosphorylation can occur. The word phosphorylation is clearly indicating that something is getting a phosphate group added to it, and nothing like this happens during the ETC. It's actually ADP that gets phosphorylated, creating (synthesizing) ATP. But phosphorylation reactions, and in fact all endergonic reactions, require a significant input of energy in order to proceed. ATP Synthase gets this required energy from a flow of protons through it, taking advantage of the work that was done by the ETC.

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