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Cellular Respiration - Conclusion

Cellular Respiration - Conclusion. The Electron Transport Chain and Oxidative Phosphorylation. Oxidative phosphorylation: when electron transport is coupled to ATP synthesis through chemiosmosis

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Cellular Respiration - Conclusion

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  1. Cellular Respiration - Conclusion The Electron Transport Chain and Oxidative Phosphorylation

  2. Oxidative phosphorylation: when electron transport is coupled to ATP synthesis through chemiosmosis • NADH and FADH2 (from glycolysis and the citric acid cycle)donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation.

  3. The electron transport chain is in the inner membrane (cristae) of the mitochondrion.

  4. Figure 9.13 NADH 50 Most of the chain’s components are proteins, which exist in multiprotein complexes. The carriers alternate reduced and oxidized states as they accept and donate electrons. Electrons drop in free energy as they go down the chain and are finally passed to O2, forming H2O. 2 e NAD FADH2 2 e Multiproteincomplexes FAD I 40 FMN II FeS FeS Q III Cyt b FeS 30 Cyt c1 IV Cyt c Free energy (G) relative to O2 (kcal/mol) Cyt a Cyt a3 20 2 e 10 (originally from NADH or FADH2) 2 H + 1/2O2 0 H2O

  5. Electrons are passed through a number of proteins including cytochromes (each with an iron atom) to O2. • The electron transport chain generates no ATP directly. • What is its purpose then?

  6. Chemiosmosis: The Energy-Coupling Mechanism • Electron transfer in the electron transport chain causes proteins to pump H+ from the mitochondrial matrix to the intermembrane space. • H+ then moves back across the membrane, passing through the protein, ATP synthase. • ATP synthase uses the exergonic flow of H+ to drive phosphorylation of ATP. • This is an example of chemiosmosis, the use of potential energy in a H+ gradient to drive cellular work.

  7. INTERMEMBRANE SPACE Figure 9.14 H Stator Rotor Internalrod Catalyticknob ADP + P i ATP MITOCHONDRIAL MATRIX

  8. 1 2 Figure 9.15 H H H Proteincomplexof electroncarriers H Cyt c IV Q III I ATPsynth-ase II 2 H + 1/2O2 H2O FAD FADH2 NAD NADH ADP  P i ATP (carrying electronsfrom food) H Electron transport chain Chemiosmosis Oxidative phosphorylation

  9. The H+ gradient is referred to as a proton-motive force, emphasizing its capacity to do work. • The potential energy from diffusion of H+ across the membrane powers the synthesis of ATP.

  10. Summary • During cellular respiration, most energy flows in this sequence: glucose  NADH  electron transport chain  proton-motive force  ATP • About 34% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about 36 ATP. • What happens to the rest of the energy? It’s given off as heat.

  11. Cellular Respiration

  12. What if there’s no oxygen? • Without O2, the electron transport chain will cease to operate. • In that case, glycolysis couples with fermentation or anaerobic respirationto produce ATP. • Anaerobic respiration: electron transport chain with an electron acceptor other than O2 (often sulfate) • Fermentation: substrate-level phosphorylation (like glycolysis)

  13. Fermentation • Fermentation = glycolysis + recycling of NAD+(to use for more glycolysis) • alcohol or lactic acid

  14. Compare + Contrast • Both do glycolysis • Both reduce NAD+(electron acceptor) • Final electron receptor is different • Cellular Respiration: O2 • Fermentation: pyruvate or acetaldehyde • Produce different amounts of ATP • Cellular respiration = 32 ATP per glucose • Fermentation = 2 ATP per glucose

  15. Glucose Figure 9.18 Glycolysis CYTOSOL Pyruvate O2 present: Aerobic cellular respiration No O2 present:Fermentation MITOCHONDRION Ethanol,lactate, orother products Acetyl CoA Citricacidcycle

  16. Other Fuel Molecules • Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration – not just glucose. • Carbohydrates  glycolysis • Proteins (amino acids)  glycolysis or the citric acid cycle • Fats • Glycerol  glycolysis • Fatty acids  acetyl CoA (Citric Acid Cycle) • An oxidized gram of fat produces more than twice as much ATP as an oxidized gram of carbohydrate.

  17. Carbohydrates Proteins Fats Figure 9.19 Aminoacids Sugars Glycerol Fattyacids Glycolysis Glucose Glyceraldehyde 3- P NH3 Pyruvate Acetyl CoA Citricacidcycle Oxidativephosphorylation

  18. With 1 molecule of glucose, cellular respiration produces 36-38 ATP molecules.

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