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Harvesting Energy: Glycolysis and Cellular Respiration Chapter 8 Using the Energy from Photosynthesis 6CO2 + 6H2O + light • Some ATP is produced in photosynthesis, but most energy is stored in sugars. • In the mitochondria of eukaryotic cells, glucose is broken down into CO2, releasing energy as ATP. C6H12O6 + 6O2 Energy Produced through the Breakdown of Glucose C6H12O6 + 6O2 + heat 6CO2 + 6H2O + ATP + heat Energy Carrier Molecules • Energy released from ATP • Three major metabolic stages that produce energy from glucose: – Glycolysis – Krebs Cycle – Electron Transport Chain (ETC) + + • H+ and electrons released from NADH NAD H NAD + H + 2e- Glycolysis Glycolysis • “To Break Apart a Sweet” • Glucose must be activated by addition of phosphate to harvest energy. • Net energy harvest = 2 ATP and 2 NADH Energy Generation through Respiration Glucose Within the cytosol 1 2 3 Fermentation • Only occurs under certain circumstances: – If no mitochondria are present. – If no O2 is available, anaerobic conditions. Glycolysis Pyruvate 1. Glucose is activated, using two ATP, by the addition of phosphate creating fructose bisphosphate. 2. Fructose bisphosphate is split into two glyceraldehyde 3phosphate molecules. 3. G3P transfers phosphates to ADP, generating ATP and pyruvate. • Regenerates NAD+ for glycolysis. • Two types of fermentation: Within mitochondria Fermentation Krebs Cycle No ATP production 32-34 ATP produced – Lactic Acid Fermentation – Alcohol Fermentation Alcohol Fermentation Alcohol Fermentation • Oxygen is not needed in fermentation (anaerobic). – Many microorganisms use glycolysis to make ATP and fermentation to regenerate NAD+ – Yeast switches to alcoholic fermentation if O2 is not available • Wine and beer • Bread holes • Sour cream, yogurt, cheese Lactic Acid Fermentation • Oxygen is not needed in fermentation (anaerobic). – Our muscle cells switch to lactic acid fermentation to generate ATP when O2 is scarce. – Lactate can cause muscle fatigue and pain. – Ultimately lactic acid converted back to pyruvate in the liver. Lactic Acid Fermentation Energy Generation through Respiration Glucose Mitochondria Glycolysis Glucose Pyruvate Glycolysis Pyruvate Within the cytosol Krebs Cycle Within mitochondria Fermentation Krebs Cycle No ATP production 32-34 ATP produced Mitochondria • “The Powerhouse of the Cell” • Possesses two membrane creating compartments. • Respiration occurs within its membrane. Electron Transport Chain Additional Energy Generation • Extracting further energy from glucose occurs in two steps. – First, pyruvate is converted into acetylCoA (coenzyme A), releasing CO2. – Net Energy Harvest = 1 NADH Krebs Cycle • Second, energy is generated through the Krebs cycle, or citric acid cycle. • An additional energy carrier molecule, FAD is utilized. • Net Energy Harvest = 1 ATP, 3 NADH, and 1 FADH2. Glucose Metabolism Krebs Cycle 1 1. Pyruvate from glycolysis is converted to acetyl-CoA, generating one NADH. 2 2. Coenzyme A is recycled producing citrate. 3. Citrate is converted to succinate, then to oxaloacetate before returning to citrate with utilizing CoA, generating three NADH, one ATP, and one FADH2. 3 Glucose Metabolism and Respiration Glycolysis: Glucose 2 pyruvate + 2 NADH + 2 ATP Formation of acetyl-CoA: 1 NADH per pyruvate (2 NADH per glucose) Krebs Cycle: 3 NADH + 1 FADH2 + 1 ATP per pyruvate (6 NADH + 2 FADH2 + 2 ATP per glucose) Total: 10 NADH + 2 FADH2 + 4 ATP per glucose Electron Transport Chain of Mitochondria •The cell produces only 4 ATP molecules during glycolysis and the Krebs cycle. •Additional high-energy electron carriers have been made (10 NADH and 2 FADH2). •Along the inner membrane of the mitochondria, electrons from NADH and FADH2 are used to generate more ATP. Electrons power H+ transport across the membrane Electrons are fed into the electron transport chain. Oxygen accepts spent electrons, making water. A high concentration gradient of H+ is generated. Mechanism of ATP Synthesis Membrane ATP Synthase, from the RCSB Protein Databank http://pdbbeta.rcsb.org Flow of H+ back across the membrane is coupled to ATP synthesis. Mechanism of ATP Synthesis Start Movie Summary Efficiency of Respiration 1. Glucose is converted into pyruvate. 2. In the absence of O2, fermentation of pyruvate occurs. 3. In the presence of O2, pyruvate is brought into the mitochondria for cellular respiration. 4. Electrons are stripped from C-molecules and fed to the ETC to generate ATP. • Cellular Respiration – 40% efficiency – ~ 60% is lost as heat • Most efficient cars – ~25% of energy stored in gasoline to energy that moves car. – ~75% lost as heat. Other organic molecules feed into glycolysis and the Krebs cycle. Process Location e- Carrier ATP per Formed Glucose Glycolysis Cytosol 2 NADH 2 ATP Cellular Respiration Mitochondrial Matrix 2 NADH none Mitochondrial 6 NADH, Matrix 2 FADH2 Electron Mitochondrial none Transport Chain Membrane Krebs Cycle 2 ATP 28-30 ATP Homework Chapter 8 Thinking Through the Concepts, Review Question 7