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| Summary |
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| Cellular respiration is the step-wise oxidation of food molecules in a cell using oxygen, producing CO2 and water and releasing energy, which is stored in ATP for later use. Cellular respiration may be aerobic or anaerobic. The initial steps constituting glycolysis are common to both. Glycolysis results in the conversion of glucose into pyruvic acid. Two molecules of ATP are gained in the process. |
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| In anaerobic respiration, molecular oxygen is not needed. The electrons removed from the substrate are transferred by the oxidoreductases to electron acceptors other than oxygen. Its end products are lactic acid or ethanol. |
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| Aerobic respiration takes place in the mitochondria and requires molecular oxygen. The process can be divided into 2 mutually dependent steps, the TCA cycle and electron transport chain. On entering the mitochondrion, pyruvic acid is oxidized to acetyl CoA. Acetyl CoA enters the TCA cycle, where it is oxidized further, yielding carbon dioxide and reduced coenzymes NADH and FADH2. The reduced coenzymes are regenerated in the electron transport chain. The electron transport enzymes of the inner mito chondrial membrane transport the electrons in an ordered sequence to molecular oxygen ultimately producing H2O. |
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| Simultaneously these enzymes transfer protons from the matrix to the outside of the inner membrane, giving rise to a proton gradient. The protons subsequently diffuse back to the matrix across the inner membrane particles. The energy released by their flow is utilized to synthesize ATP by the ATP synthase present in the F0 - F1 complex. The process is termed oxidative phosphorylation. The energy trapped in the high energy bonds of ATP is utilized to drive the energy requiring processes of the body. |
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| Complete oxidation of a glucose molecule to CO2 and H2O takes just a second, and produces 36 or 38 ATP molecules. |
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| Some organisms oxidize glucose by the PPP pathway. |
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