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Transcript
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 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 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” Overview of Cellular Respiration Glucose is broken down yielding energy Breakdown is catabolic Synthesis or build –up is anabolic Overview of Cell Respiration Cell respiration stores energy in ATP molecules overall equation: C6H12O6 + 6O2 ----> 6CO2 + 6H2O + energy efficiency ~40% compared with car ~25% Energy is used for body maintenance and voluntary activity average human needs ~2200kcal/day 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 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 each step breakdown portion oxidized and NAD+ reduced to NADH at 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 Molecular Basics: Two mechs to make ATP Two mechanisms for making ATP 1. Chemiosmosis involves electron transport chain and ATP synthase uses potential energy of H+ gradient produced by electron transport chain to generate ATP Two mechs to make ATP cont. 2. Substrate-level phosphorylation does not involve either electron transport chain or ATP synthase phosphorylated by enzyme using PO4group from phosphorylated substrate ADP When an electron or hydrogen is lost, this is known as: A. B. Oxidation Reduction Three Stages of Respiration Glycolysis- in the cytoplasm Kreb’s cycle-in the mitochondrial matrix Electron transport chain-in the inner mitochondrial membrane ….. Glycolysis Harvests energy by oxidizing glucose to pyruvic acid in cytoplasm ten steps involved separate enzyme for each step also requires ADP, phosphate and NAD+ ATP required to form initial intermediates Summary of Glycolysis broken steps into two phases: 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 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 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 ADP, phosphate, NAD+, FAD, and oxaloacetate eighth step regenerates oxaloacetate requires 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 meatbolism SO.. For each Acetyl CoA that enters the Krebs Cycle how many ATP, FADH2 and NADH are made From Glycolysis FADH is made? A. B. True False Electron Transport Chain The Electron Transport Chain is imbedded 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 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 Chemiosmosis: ATP is Generated H+ gradient drives ATP synthesis in matrix as H+ transported through ATP synthase net energy gain is 34 ATP for each glucose Oxygen is the final hydrogen( electron) acceptor Water is the “waste” product 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 Cellular Respiration: Summary Each glucose molecule yields 38 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 some 2 ATP, but mostly strips out CO2 and produces energy shuttles Electron present transport chain produces 34 ATP but only if O2 Cellular Respiration: Summary cont. 3 ATP produced for each NADH and 2 ATP produced for each FADH2 Don’t try to derive each one, there is still scientific controvery about this issue The transporters of the Electron Transport Chain are antiports: A. B. True False Some things to consider ??????????? Why do you breathe oxygen? When you diet where do those “lost” pounds go and how do they do it? Where does the CO2 you exhale come from? 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 pyruvate represents decision point in respiratory pathway for organisms capable of carrying out either aerobic respiration or fermentation strict anaerobes live in environments that lack oxygen; only glycolysis facultative anaerobes, e.g. yeast and certain bacteria, live in environments that either lack or contain oxygen Molecular Fuel for Respiration Free glucose not common in animal diets Each basic food type can be molecular energy source carbohydrates hydrolyzed to glucose; enters glycolysis proteins hydrolyzed to amino acids amino group stripped and eliminated in urine carbon backbone enters middle of glycolysis or Kreb’s cycle lipids hydrolyzed to glycerol and fatty acids glycerol enters middle of glycolysis fatty acids converted to acetyl CoA; enters Kreb’s cycle Raw Materials for Biosynthesis Cells obtain raw materials directly from digestion of macromolecules Assembly of new molecules often reversal of breakdown during respiration ATP required for biosynthesis and produced by degradation All cells can harvest molecular energy Storage of molecular energy restricted