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Harvesting Chemical Energy

Harvesting Chemical Energy. Chapter 9. Objectives. Describe how covalent bonds serve as an energy store Describe the relationship between form and function Relate the caloric requirements of humans to the energy requirements for cellular reactions

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Harvesting Chemical Energy

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  1. Harvesting Chemical Energy Chapter 9

  2. Objectives • Describe how covalent bonds serve as an energy store • Describe the relationship between form and function • Relate the caloric requirements of humans to the energy requirements for cellular reactions • Describe the workings of each phase of cellular respiration with emphasis on the reactants, the products, the net production of ATP and the cellular locations • Explain how alcoholic fermentation and lactic acid fermentation can be used to generate ATP in the absence of oxygen

  3. Introduction • Harvesting chemical energy involves mitochondria • Generates ATP • With adequate O2 supplies, food is “burnt” (aerobic respiration) • In absence of O2, food molecules are “fermented”

  4. Overview of Cellular Respiration • Glucose is broken down yielding energy • Breakdown is catabolic • Synthesis or build –up is anabolic

  5. Overview of Cellular Respiration • Cellular respiration stores energy in ATP molecules Overall equation: C6H12O6 + 6O2 ----> 6CO2 + 6H2O + energy • Efficiency ~40% • Energy efficiency of car= ~25% • Energy is used for body maintenance and voluntary activity • Average human needs ~2200kcal/day

  6. Molecular Basics • Energy obtained by transferring electrons (Hydrogens) from organic molecules to oxygen • movement of H+ represents electron movement • involves series of steps coupling endergonic and exergonic reactions

  7. Molecular Basics • Hydrogen carriers (like NAD+) shuttle electrons • paired endergonic-exergonic reactions are known as redox (reduction-oxidation) reactions • oxidation-loss of electron, exergonic • reduction-gain of electron, endergonic • breakdown of glucose involves series of redox reactions • at each step breakdown portion oxidized and NAD+ reduced to NADH

  8. Molecular Basics • Energy released when electrons “fall” from hydrogen carrier to oxygen • NADH releases energetic electrons, regenerating NAD+ • electrons enter electron transport chain • series of redox reactions, passes electrons from one molecule to next • ultimate electron acceptor is oxygen • small amounts of energy released to make ATP

  9. Molecular Basics: Two mechs to makeATP 1. Chemiosmosis • involves electron transport chain and ATP synthase • uses potential energy of H+ gradient produced by electron transport chain to generate ATP • ATP synthesis occurs through oxidative phosphorylation • ADP is phosphorylated (phosphorous is added to it) with a free (unbound) phosphorous. • powered by the redox reactions of the ETC

  10. Two mechs to make ATP cont. 2. Substrate-level phosphorylation • does not involve either electron transport chain or ATP synthase • ADP phosphorylated by enzyme using PO4- group from phosphorylated substrate

  11. When an electron or hydrogen is lost, this is known as: • Oxidation • Reduction

  12. Three Stages of Respiration • Glycolysis- in the cytoplasm • Kreb’s cycle-in the mitochondrial matrix • Electron transport chain-in the inner mitochondrial membrane …..

  13. Glycolysis • Harvests energy by oxidizing glucose to pyruvic acid in cytoplasm • 10 steps involved • separate enzyme for each step • also requires ADP, phosphate and NAD+ • ATP required to form initial intermediates

  14. Summary of Glycolysis Two phases: • Steps 1-5 are endergonic = require ATP input • Steps 6-10 are energy-releasing= exergonic; make ATP and NADH • net energy gain is 2 ATP and 2 NADH for each glucose • 2 Pyruvate are also made

  15. Pyruvate is processed to Acetyl Co A • Pyruvate is chemically processed before entering Kreb’s cycle • NAD+ is reduced to to NADH • Pyruvate is stripped of a carbon, releases CO2 • complexed with coenzyme A (CoA) forming acetyl CoA • net energy gain is 2 NADH for each glucose

  16. Kreb’s Cycle • Completes oxidation of organic molecules, releasing many NADH and FADH • occurs in mitochondrial matrix • involves eight steps which results in production of CO2 as waste product • requires ADP, phosphate, NAD+, FAD, and oxaloacetate • eighth step regenerates oxaloacetate

  17. Krebs Cycle Summary • Net energy gain from Krebs is 2 ATP, 6 NADH and 2 FADH2 for each glucose that started the process of cellular metabolism • SO.. for each Acetyl CoA that enters the Krebs Cycle how many ATP, FADH2 and NADH are made?

  18. From Glycolysis FADH is made? • True • False

  19. Electron Transport Chain • The Electron Transport Chain is embedded in the mitochondrial cristae • There are many proteins involved that transfer hydrogens to generate a hydrogen gradient • Chemiosmosis= the process in which energy stored in the form of a hydrogen gradient is used to power ATP synthesis • The greatest amount of energy is produced via this method

  20. Electron Transport Chain: Gradient Is Generated • Electron transport chain is series of protein complexes in the inner mitochondrial membrane (cristae) • complexes oscillate between reduced and oxidized state • H+ transported from inside cristae to intermembrane space as redox occurs

  21. Free energy change during electron transport • Overall energy drop= 53 kcal/mol • Occurs as a series of small steps • Releases energy in small amounts

  22. Chemiosmosis: ATP is Generated • H+ gradient drives ATP synthesis in matrix as H+ transported through ATP synthase • net energy gain is 28 ATP for each glucose • Oxygen is the final hydrogen( electron) acceptor • Water is the “waste” product

  23. Electron Transport Chain: Issues • Some poisons function by interrupting critical events in respiration rotenone, cyanide and carbon monoxide block various parts of electron transport chain oligomycin blocks passage of H+ through ATP synthase Uncouplers, like dinitrophenol (DNP), cause cristae to leak H+, cannot maintain H+ gradient

  24. Cellular Respiration: Summary • Each glucose molecule yields ~32 ATP • glycolysis in cytoplasm yields 2 ATP in absence of O2, but mostly prepares for mitochondrial steps that require O2 • Kreb’s cycle in mitochondrial matrix produces 2 ATP, but mostly strips out CO2 and produces energy shuttles • Electron transport chain produces 28 ATP but only if O2 present

  25. Cellular Respiration: Summary cont. • 2.5 ATP produced for each NADH and 1.5 ATP produced for each FADH2 • Don’t try to derive each one, there is still scientific controversy about this issue

  26. Some things to consider ??????????? • Why do you breathe oxygen? • Why do you get hot when you exercise? • Where does the CO2 you exhale come from?

  27. Fermentation • Energy-releasing reactions in absence of oxygen • Recharges NAD+ pool so glycolysis can continue in absence of oxygen • alcoholic fermentation in yeast and bacteria results in 2C ethanol; product is toxic • lactic acid fermentation in many animals and bacteria results in 3C lactic acid; causes muscle fatigue

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