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How Cells Release Stored Energy

How Cells Release Stored Energy. Chapter 9. When a molecule has hydrogen, it has more energy and removing them releases the energy. The energy produced from the "burning" of glucose is used to make ATP. In chemistry this process is called the oxidation of glucose.

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How Cells Release Stored Energy

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  1. How Cells Release Stored Energy Chapter 9

  2. When a molecule has hydrogen, it has more energy and removing them releases the energy. The energy produced from the "burning" of glucose is used to make ATP. In chemistry this process is called the oxidation of glucose. The hydrogen carriers NAD and FAD are used to help release the energy in glucose by moving hydrogens and electrons around.

  3. Glucose • A simple sugar (C6H12O6) • Atoms held together by covalent bonds In-text figurePage 136

  4. Summary Equation for Aerobic Respiration C6H1206 + 6O2 6CO2 + 6H20 glucose oxygen carbon water dioxide

  5. Glycolysis -in cytoplasm -does not use oxygenOccurs in Two Stages • Energy-requiring steps • ATP energy activates glucose and its six-carbon derivatives • Actually uses 2 ATP’s • Energy-releasing steps • The products of the first part are split into 2 three carbon pyruvate molecules • 4 ATP and 2NADH form • 4 ATP’s form – 2 ATP’s used = 2 net ATP’s made

  6. Glycolysis is often called anaerobic respriation because it does not need oxygen. This process occurs in the cytoplasm. Two net molecules of ATP are made for cell use. It involves glucose being converted to two molecules of pyruvic acid (or pyruvate). This process is not very efficient at converting the energy of glucose into ATP as only 2 ADP are phosphorylated instead of 32 as in Krebs and chemiosmosis.

  7. Energy-Requiring Steps of Glycolysis 2 ATP invested glucose ADP ATP ATP P P P P P P glucose-6-phosphate fructose-6-phosphate ADP fructose1,6-bisphosphate PGAL PGAL Energy-Requiring Steps Figure 8.4(2)Page 137

  8. ATP ATP ATP ATP P P P P P P P P P P P P PGAL PGAL NAD+ NAD+ Energy-Releasing Steps NADH NADH Pi Pi 1,3-bisphosphoglycerate 1,3-bisphosphoglycerate ADP ADP Phosphorylations 3-phosphoglycerate 3-phosphoglycerate 2-phosphoglycerate 2-phosphoglycerate H2O H2O PEP PEP ADP ADP pyruvate pyruvate Figure 8.4 Page 137

  9. Glycolysis: Net Energy Yield Energy requiring steps: 2 ATP invested Energy releasing steps: 2 NADH formed 4 ATP formed Net yield is 2 ATP, 2 pyruvic acid and 2 NADH

  10. After glycolysis: -If oxygen is present, the pyruvic acid will go into the mitochondria where the Kreb’s cycle (or citric acid cycle) is performed followed by the ETC. This allows the rest of the energy stored in the hydrogen to be extracted. -If no there is no oxygen, then the Kreb's cycle can not be completed (or started in some organisms). A cell can continue doing glycolysis in the absence of oxygen to produce some ATP, BUT it must regenerate NAD to keep glycolysis going. This is called anaerobic respiration (or fermentation). Pyruvate will form either lactic acid (muscles) or ethanol (bacteria, yeast or plants). In either case NAD is regenerated so that glycolysis can continue.

  11. Fermentation Pathways • Begin with glycolysis • Do not break glucose down completely to carbon dioxide and water • Yield only the 2 ATP from glycolysis • Steps that follow glycolysis serve only to regenerate NAD+

  12. Lactate Fermentation GLYCOLYSIS C6H12O6 ATP 2 energy input 2 NAD+ 2 ADP NADH 2 ATP 4 2 pyruvate energy output 2 ATP net LACTATE FORMATION electrons, hydrogen from NADH 2 lactate

  13. GLYCOLYSIS C6H12O6 Alcoholic Fermentation 2 ATP 2 NAD+ energy input 2 ADP NADH 2 ATP 4 2 pyruvate energy output 2 ATP net ETHANOL FORMATION 2 H2O 2 CO2 2 acetaldehyde electrons, hydrogen from NADH 2 ethanol

  14. Anaerobic Electron Transport • Carried out by certain bacteria • Electron transfer chain is in bacterial plasma membrane • Final electron acceptor is compound from environment (such as nitrate), not oxygen • ATP yield is low

  15. After glysolysis, if oxygen is present aerobic respiration proceeds in the mitochondria.

  16. O O PreparatorySteps Ex. 2 • Preparatory reactions • Pyruvate is decarboxylated and oxidized (releasing carbon dioxide) • NAD+ is reduced • Acetyl Co-A is formed • Ex. 1 pyruvate coenzyme A (CoA) NAD+ carbon dioxide NADH acetyl-CoA

  17. Overall Products Coenzyme A 2 CO2 3 NADH FADH2 ATP Overall Reactants Acetyl-CoA 3 NAD+ FAD ADP and Pi The Krebs Cycle

  18. The enzymes for Kreb's is found in the inner compartment of the mitochondria. Summary of Krebs- Occurs in Mitochondria 2X's Pyruvate---> 3 CO2 6 CO2 1 ADP ---> 1 ATP 2 ATP 4 NAD ---> 4 NADH 8 NADH 1 FAD ---> 1 FADH2 2 FADH2 (also, oxaloacetate regenerates so cycle can continue)

  19. Coenzyme Reductions during First Two Stages • Glycolysis 2 NADH • Preparatory reactions 2 NADH • Krebs cycle 2 FADH2 + 6 NADH • Total 2 FADH2 + 10 NADH

  20. Electron Transfer Phosphorylation • Occurs in the mitochondria • Coenzymes deliver electrons to electron transfer chains • Electron transfer sets up H+ ion gradients • Flow of H+ down gradients powers ATP formation (chemiosmotic)

  21. The purpose of chemiosmosis is to extract the energy found in NADH and FADH2 to make more ATP. This involves the cristae. There are electron transport chains that are used. The electrons from the NADH and FADH2 are used to move on the electron transport chain. As the electrons move down the electron transport chain, H+ ions are pumped across the membrane. The electrons from one NADH can pump 6 H+ across the membrane, but the electrons from FADH2 can only pump 4 H+ across the membrane.

  22. Creating an H+ Gradient OUTER COMPARTMENT NADH INNER COMPARTMENT

  23. The outer compartment of the mitochondria becomes positive and the inside becomes negative like a battery. This "battery" can do work. The hydrogen ions can cross an F1 particle and make ATP. It takes 2 H+ to cross the F1 particle to provide enough energy to make ATP.

  24. Making ATP: Chemiosmotic Model ATP INNER COMPARTMENT ADP+Pi

  25. Summary 8 NADH2 x 6 H = 48 H+ 2 FADH2(Krebs)x 4 H = 8 H+ 2 FADH2(glyc.) X 4 H = 8 H+ 64 H+ 64 H+ --> 32 ATP

  26. Importance of Oxygen • Electron transport phosphorylation requires the presence of oxygen • Oxygen withdraws spent electrons from the electron transfer chain, then combines with H+ to form water

  27. Summary of Energy Harvest(per molecule of glucose) • Glycolysis • 2 ATP formed by substrate-level phosphorylation • Krebs cycle and preparatory reactions • 2 ATP formed by substrate-level phosphorylation • Electron transport phosphorylation • 32 ATP formed

  28. CYTOPLASM glucose ATP 4 Overview of Aerobic Respiration 2 ATP Glycolysis e- + H+ (2 ATP net) 2 pyruvate 2 NADH e- + H+ 2 CO2 2 NADH e- + H+ 4 CO2 8 NADH KrebsCycle e- + H+ 2 ATP 2 FADH2 e- Electron Transfer Phosphorylation 32 ATP H+ water e- +oxygen Typical Energy Yield: 36 ATP Figure 8.3Page 135

  29. Efficiency of Aerobic Respiration • 686 kcal of energy are released • 7.5 kcal are conserved in each ATP • When 36 ATP form, 270 kcal (36 X 7.5) are captured in ATP • Efficiency is 270 / 686 X 100 = 39 percent (at best) • Most energy is lost as heat

  30. **Fats/Lipids = Glycerol and 3 fatty acids Glycerol is converted to PGAL and respired in glycolysis. The fatty acids are chopped into 2 carbon acetyl groups and used in the Krebs or citric acid cycle. **Proteins = amino acids The amino acids are sent to the liver where the liver removes the amine group. The left over acid is then used at some point in the Krebs cycle.

  31. FOOD Alternative Energy Sources fats glycogen complex carbohydrates proteins simple sugars fatty acids glycerol amino acids glucose-6-phosphate NH3 carbon backbones GLYCOLYSIS urea PGAL pyruvate acetyl-CoA Other organic molecules can be involved in respiration. KREBS CYCLE Figure 8.11Page 145

  32. Evolution of Metabolic Pathways • When life originated, atmosphere had little (none) free oxygen • Earliest organisms used anaerobic pathways • Later, noncyclic pathway of photosynthesis increased atmospheric oxygen • Cells arose that used oxygen as final acceptor in electron transport and were more efficient

  33. Processes Are Linked sunlight energy PHOTOSYNTHESIS water + carbondioxide sugarmolecules oxygen AEROBICRESPIRATION In-text figurePage 146

  34. Photosynthesis Energy-storing pathway Releases oxygen Requires carbon dioxide Makes carbs Aerobic Respiration Energy-releasing pathway Requires oxygen Releases carbon dioxide Breaks carbs Linked Processes

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