Oxidative phosphorylation is the metabolic pathway in which cells use enzymes to oxidize nutrients, thereby releasing energy that is used to produce adenosine triphosphate (ATP). Simply put, it's how your cells make the energy currency they need to function.
The Process Explained
Oxidative phosphorylation is a multi-step process that occurs in the inner mitochondrial membrane of eukaryotic cells (and in the cell membrane of prokaryotes). Here’s a breakdown:
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Electron Transport Chain (ETC): This is a series of protein complexes (Complex I, II, III, and IV) embedded in the inner mitochondrial membrane.
- Electrons from molecules like NADH and FADH2 (produced during glycolysis, the citric acid cycle, and fatty acid oxidation) are passed along these complexes. As stated in the reference, "electrons derived from NADH and FADH2 combine with O2."
- This electron transfer releases energy.
- The final electron acceptor in the chain is oxygen (O2), which gets reduced to form water (H2O).
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Proton Pumping: As electrons move through Complexes I, III, and IV, protons (H+) are pumped from the mitochondrial matrix into the intermembrane space.
- This creates an electrochemical gradient, with a higher concentration of protons in the intermembrane space and a lower concentration in the matrix. This gradient stores potential energy.
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ATP Synthase: The proton gradient drives ATP synthesis through an enzyme called ATP synthase (Complex V).
- Protons flow down their concentration gradient, from the intermembrane space back into the matrix, through ATP synthase.
- This flow of protons provides the energy for ATP synthase to catalyze the reaction of ADP and inorganic phosphate (Pi) to form ATP. The reference states that the energy released "is used to drive the synthesis of ATP from ADP."
Summary Table
| Component | Function |
|---|---|
| Electron Transport Chain | Transfers electrons from NADH and FADH2 to oxygen, releasing energy. |
| Proton Pumping | Creates a proton gradient across the inner mitochondrial membrane. |
| ATP Synthase | Uses the proton gradient to synthesize ATP from ADP and inorganic phosphate. |
| NADH & FADH2 | Electron carriers that provide electrons to the ETC. |
| Oxygen (O2) | Final electron acceptor in the ETC, reduced to water (H2O). |
| ATP | The energy currency of the cell, produced by ATP synthase. |
In essence:
Electrons from NADH and FADH2 are passed down an electron transport chain, releasing energy that is used to pump protons and create an electrochemical gradient. This gradient then drives ATP synthase to produce ATP. Oxygen is the final electron acceptor.
