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CHAPTER 9: CELLULAR RESPIRATION

CHAPTER 9: CELLULAR RESPIRATION. Overview  Life is work. 9.1  Catabolic pathways yield energy by oxidizing organic fuels I. Catabolic pathways & production of ATP A. Intro 1. What allows an organic molecule to posses potential energy?

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CHAPTER 9: CELLULAR RESPIRATION

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  1. CHAPTER 9: CELLULAR RESPIRATION Overview Life is work 9.1 Catabolic pathways yield energy by oxidizing organic fuels I. Catabolic pathways & production of ATP A. Intro 1. What allows an organic molecule to posses potential energy? 2. Where is the potential energy stored in an organic molecule? a. How is the energy stored in bonds released ? 1. What helps do this? 3. Cellular respiration (catabolic rxn) a. Aerobic and anaerobic processes 1. Synonymous w/ aerobic b. Aerobic 1. O2 as one reactant Organic compounds + O2 CO2 + H2O + Energy

  2. 2. Most common fuel/organic compound used a. Glucose 3. Exergonic ∆G= -686 Kcal/mole a. Products store less free energy than reactants C6H12O6 + 6O2 6CO2 + 6H2O + Energy (ATP + heat) II. Redox reactions: Oxidation & reduction A. How does aerobic respiration yield energy? 1. Transfer of electrons a. Transfer of electrons releases stored energy 1. Used to synthesize ATP B. The principle of redox 1. The transfer of electrons from 1 reactant to another 2. Oxidation a. The loss of an electron 3. Reduction a. The gain of electrons 4. Oxidation & reduction always go together

  3. C. Oxidation of organic fuel molecules during cellular respiration C6H12O6 + 6O26CO2 + 6 H2O + Energy 1. C6H12O6 looses electrons (in the form of H) to O2 a. C6H12O6 converted to CO2 2. O2 gains electrons (in the form of H) from C6H12O6 a. O2 converted to H2O Oxidation Reduction D. Stepwise energy harvest via NAD+ & the electron transport chain 1. Oxidizing C6H12O6 CO2 + H2O happens in steps a. Controlled (steps) vs. Uncontrolled 1. “Burning” wood a. A rxn that releases potential energy b. Uncontrolled 1. Energy released in a single chemical rxn 2. Wood Light & heat

  4. 2. “Burning” food a. A rxn that releases potential energy b. Controlled 1. Energy released during several steps 2. Product of one rxn becomes the reactant in the next step of the rxn 2. NAD+ a. Electron acceptor for glucose redox rxn 1. Little energy loss in transfer b. Reduced c. Represents stored energy d. “Shuttles” electrons to electron transport chain 1. A series of redox reactions that releases small amounts of energy used to sythesize ATP

  5. 9.2 Glycolysis harvests chemical energy by oxidizing glucose to pyruvate I. Mitochondria structure II. Glycolysis A. Anaerobic stage of cellular respiration 1. Does not require O2 B. Occurs outside the mitochondria 1. Cytosol C. Glucose 2 pyruvic acid molecules 1. A 3-carbon molecule D. Energy 1. 2 ATP molecules are needed to split glucose 2. 4 ATP molecules formed by energy released from splitting glucose 3. A net gain of 2 ATP 4. 2 NADH molecules released E. Pyruvate now formed 1. If O2 present enters citric acid cycle 2. If no O2 present enters fermentation

  6. F. Glycolysis is only 3.5 % efficient 1. For every glucose molecule broken down by glycolysis only 3.5% is converted to energy 9.3 The citric acid cycle completes the energy-yielding oxidation of organic molecules I. Completes the energy-yielding oxidation of organic molecules II. Aerobic respiration A. Occurs within the mitochondria B. Pyruvate Acetyl-CoA (mitochondrial matrix) 1. The junction between glycolysis & citric acid cycle 2. Pyruvate enters mitochondria via active transport C. Pyruvate is oxidized to Acetyl CoA 1. 1 NADH & CO2 formed/Pyruvate

  7. D. The Krebs Cycle/Citric Acid Cycle 1. Acetyl CoA enters the Krebs cycle 2. Through a series of 5 main steps a. 3 NADH released/ Acetyl CoA b. 1 FADH2 released/ Acetyl CoA c. 1 ATP released/ Acetyl CoA d. 2 CO2 Remember: For every glucose molecule entering glycolysis, 2 pyruvic acid molecules are created. This in turn creates 2 acetyl CoA molecules. This results in: 2 NADH Pyruvic Acid 2 NADH Pyruvate  Acetyl CoA 2 CO2 Pyruvate  Acetyl CoA 6 NADH 2 FADH2 Kreb Cycle 2 ATP 4 CO2 For each glucose molecule

  8. 9.4 During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis I. Intro A. 2 Stages 1. Electron Transport Chain 2. Chemiosmosis B. NADH & FADH2 1. Link glycolysis & citric acid cycle to oxidative phosphorylation a. Oxidative phosphorylation 1. The production of ATP using energy derived from the redox reactions of an electron transport chain II. The pathway of electron transport A. Defined 1. Series of electron carrier molecules that shuttle electrons from 1 carrier to another releasing small, manageable amounts of energy that is used to synthesize ATP a. Does not make ATP directly

  9. B. Location 1. Inner membrane of mitochondria a. The convoluted nature of the membrane creating the cristae greatly increases SA thus increasing the # of electron transport chains 1. 1,000’s C. Structure 1. Composed of proteins embedded in inner membrane a. Proteins exist as multiprotein complexes 1. # I-IV D. Process (redox rxn) 1. Electrons enter transport chain 2. Electrons get passed from complex I IV a. 1 complex oxidized while the next in sequence is reduced

  10. 3. Small manageable amount of energy released 4. Electrons leave complex IV and are accepted by O2 forming H2O

  11. E. ATP Production 1. For every NADH 3 ATP made 2. For every FADH2 2 ATP made 3. Total ATP production 34 ATP

  12. III. Chemiosmosis: The energy coupling mechanism A. How does electron transport chain provide energy used to indirectly synthesize ATP 1. By establishing a H+ (proton) gradient 2. Protein complex I, III, IV a. Utilize the energy released by electrons to pump H+ across the inner membrane into the intermembrane space 1. Establishes a H+ gradient a. High [ ] intermembrane space b. Low [ ] matrix

  13. 3. Proton-motive force a. The capacity of the H+ gradient to perform work due to the difference in [ ] b. The potential energy stored in the form of an electrochemical gradient, generated by the pumping of H+ across a biological membrane

  14. 4. Summary a. The job of the electron transport chain is to pump H+ across inner membrane into intermembrane space 1. Uses the exergonic flow of electrons from NADH & FADH2 to pump H+ across membrane b. Creates the proton-motive force B. ATP Synthase 1. A protein complex in the inner membrane a. The only site that provides a route for H+ to diffuse down it’s gradient b. The actual enzyme that makes ATP 2. Uses the potential energy created by the H+ gradient to power ATP synthesis a. Uses the proton-motive force

  15. C. Chemiosmosis 1. An energy coupling mechanism that uses energy stored in the form of an H+ gradient across a membrane to drive cellular work IV. An accounting of ATP by cellular respiration

  16. How efficient is aerobic respiration? 66% efficient For every glucose molecule that enters aerobic respiration, 66% is converted to usable energy!! Comparison An automobile is only 25% efficient

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