![]() Roman numbered protein complexes along with Coenzyme Q (just “Q” in the drawing) and cytochrome C (Cyt c) constitute the ETC), the sequence of reactions that oxidize NADH or FADH2 to NAD and FAD (respectively). The protons end up outside the mitochondrial matrix because they are pumped across the cristal membrane using the free energy of electron transport.Įlectron transport and oxidative phosphorylation are summarized in the illustration below.ġ61 Electron Transport Oxidizes Reduced Electron Carriersġ62 Finding the Free Energy of Electron Transportġ63 Separating Electron Transport from Oxidative Phosphorylation The end products of electron transport are NAD , FAD, water and protons. Here we focus on the details of respiration as it occurs in the mitochondria of eukaryotic cells. You can read Mitchell’s original proposal of the chemiosmosis model of mitochondrial ATP synthesis in Mitchell P (1961) Coupling of phosphorylation to electron and hydrogen transfer by a chemiosmotic type of mechanism. For this insight, Peter Mitchell won the Nobel Prize in Chemistry in 1978. The Chemiosmotic Mechanism explained how the creation of an electrochemical gradient and how gradient free energy ends up in ATP. In photosynthesis, electron transfer reduces CO2 to sugars. In aerobic respiration, electrons are ultimately transferred from components at the end of the ETC to a final electron acceptor molecular oxygen, O2, making water. That gradient free energy is captured in ATP synthesis reactions coupled to the flow (diffusion) of protons back across the membrane in the process called oxidative phosphorylation. In a kind of shorthand, we say that the free energy once in reduced substrates is now in an electrochemical gradient. Since protons are charged, the proton gradient is also an electrical gradient. The result is a chemical gradient of H ions as well as a pH gradient. In both cases, free energy released when the redox reactions of an ETC are coupled to the active transport of protons (H ions) across a membrane. In plants and other photosynthetic organisms, an ETC serves to oxidize NADPH (a phosphorylated version of the electron carrier NADH). In the mitochondrial ETC, electrons flow when the reduced electron (NADH, FADH2) are oxidized. In the case of the battery, the electron flow releases free energy to power a motor, light, cell phone, etc. The electron flow from reduced substrates through an ETC is like the movement of electrons between the poles of a battery. \)Īll cells use an electron transport chain (ETC) to oxidize substrates in exergonic reactions. ![]()
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