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An evolutionary approach to learning energy metabolism

Explore how cells obtain energy through oxidation-reduction reactions to produce ATP. Learn about oxidative phosphorylation and the role of electron carriers like NADH. Understand the respiration of glucose and the transfer of electrons in the electron transport chain. Discover the different sources of energy and carbon in organisms. Dive into chemiosmosis and the role of proton gradients in ATP synthesis. Gain insights into the electron transport chain in mitochondria and the functioning of ATP synthase.

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An evolutionary approach to learning energy metabolism

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  1. An evolutionary approach to learning energy metabolism • How do cells obtain energy to make ATP? • oxidation-reduction • How do cells make ATP? • oxidative phosphorylation Images in this video are from Wikipedia, unless otherwise indicated.

  2. Oxidation-reduction is the core of energy metabolism Oxidation is the loss of electrons Organic molecules (food) and inorganic chemical electron donors are oxidized Reduction is the gain of electrons The amount of free energy released depends on the reduction potential difference of the redox pair Catabolic pathways feature a series of redox reactions (electron-transfer reactions) NAD+/NADH is the primary electron carrier

  3. Summary of respiration of glucose • C6H12O6 + 6O2 6CO2 + 6H2O • C6H12O6 + 6O2 + 6H2O  6CO2 + 12H2O • C is oxidized to CO2 • O2 is reduced to H2O • Electrons are transferred from glucose to O2 via NADH

  4. NAD = nicotinamide adenine dinucleotide. For NADH + H+ +1/2 O2↔ NAD+ + H2O, ΔGo = -52.4 kcal/mol. Oxidized and reduced forms of NAD

  5. Hydrogen powers ATP synthesis

  6. Respiration: transfer of electrons from electron donors to electron acceptors to charge a membrane proton gradient H+ electrochemical gradient H+ Electron transport chain membrane NADH Terminal electron acceptors O2, NO3-, SO42-, Mn4+, Fe3+, CO2, etc. NAD+ Electron donors {[CH2O], H2, H2S, CH4, Fe2+, etc.} Diagram by J. Choi

  7. Organisms may be classified by the source of energy and the source of organic carbon: • Heterotrophs – both energy and carbon come from organic molecules (food) • Autotrophs – make their own organic carbon from CO2 • Photoautotrophs – energy from sunlight • Chemoautotrophs – energy from reduced inorganic molecules

  8. Terminal Electron Acceptors Different e- acceptors are used sequentially in microbial ecosystems. O2 ∆G = -479 kJ mol-1 NO3- ∆G = -453 kJ mol-1 Mn4+ ∆G = -349 kJ mol-1 Fe3+ ∆G = -114 kJ mol-1 SO42- ∆G = -77 kJ mol-1

  9. Chemiosmosis in prokaryotes Electron transport chain generates proton gradient across membrane. Resulting proton motive force drives ATP synthesis and active transport. Fenchel, Origin & Early Evolution of Life, Oxford U Press 2002, Fig 6.2

  10. Electron transport chain in mitochondria

  11. Proton gradient powers ATP synthase during respiration (oxidative phosphorylation) F0 F0 portion in membrane • resembles flagellar motor F1 portion (ATP synthase) -resembles DNA helicase www.youtube.com/watch?v=KU-B7G6anqw F1

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