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CHAPTER 23

CHAPTER 23. Metabolism and Energy Production. What happens after glycolysis?. When oxygen is present (under aerobic conditions)… The acetyl-CoA is sent into the citric acid cycle, which is followed by the electron transport chain. The latter process makes most of the ATP.

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CHAPTER 23

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  1. CHAPTER 23 Metabolism and Energy Production

  2. What happens after glycolysis? • When oxygen is present (under aerobic conditions)… • The acetyl-CoA is sent into the citric acid cycle, which is followed by the electron transport chain. • The latter process makes most of the ATP.

  3. A. The Citric Acid Cycle • Overall, a series of reactions that degrade acetyl-CoA to CO2 and energy • This energy is used to produce NADH and FADH2 • NADH and FADH2 are the “electron limousines” that shuttle the electrons to the electron transport chain, where they are used to generate a lot of ATP.

  4. Summary of Products: Citric Acid Cycle • You get… • 2 CO2 • 3 NADH • 1 FADH2 • 1 GTP which is used to form ATP • **These are the products from ONE acetyl-CoA. Double those numbers if you are considering the products from one glucose molecule through the whole process.

  5. Citric Acid Cycle Regulation • Function of citric acid cycle: generate ATP • So, when the cell needs energy, pyruvate is converted to acetyl-CoA, and the citric acid cycle proceeds. • But when the cell has sufficient energy, there is not much conversion to acetyl-CoA, and the citric acid cycle slows.

  6. B. Electron Carriers • What have we obtained so far in terms of energy-carrying molecules? From One Glucose ATP Coenzymes Glycolysis 2 2 NADH 2 pyruvate --> 2 acetyl-CoA 2 NADH Citric acid cycle 2 6 NADH 2 FADH2

  7. How Do The Electron Carriers Work? • After glycolysis and the citric acid cycle, these carriers are in the reduced form. • As they are oxidized later on, they provide energy for the synthesis of ATP. • In the electron transport chain (which follows the citric acid cycle), electrons are passed from one intermembrane protein to the next until they combine with oxygen to form H2O. http://www.science.smith.edu/departments/Biology/Bio231/etc.html

  8. C. Oxidative Phosphorylation and ATP • Oxidative phosphorylation: the production of ATP from ADP and Pi using the energy released during the electron transport chain • Chemiosmotic model links this energy to a proton gradient. • As electrons are passed along the chain, H+ is passed into the intermembrane space. • A proton gradient is created, whereby the intermembrane space has both a positive charge and a lower pH. • The energy generated by this gradient is used by ATP synthase to drive the synthesis of ATP.

  9. Creation of Proton Gradient

  10. D. ATP Energy from Glucose • How much ATP do you get from all of these processes? • ATP from glycolysis: • 2 NADH (which, long-term, give you 4 ATP) + 2 ATP = 6 ATP • Conversion of pyruvate --> acetyl-CoA: • 2 NADH (one per pyruvate) = 6 ATP • Citric acid cycle • From each acetyl-CoA: 3 NADH, one FADH2, one ATP which will, total, give 24 ATP • The combination of it all: 36 ATP per glucose.

  11. Oxidation of Glucose

  12. What Happens To All This Glucose? • If there is extra glucose around -- in excess of what our cells need for energy -- what happens to it? • If glucose levels in the brain or blood get low, what does the body do? • Glucose can also be synthesized from non-carbohydrate sources as needed.

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