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Chapter 9 Cellular Respiration: Harvesting Chemical Energy

Chapter 9 Cellular Respiration: Harvesting Chemical Energy. Introduction. Energy for work enters as LIGHT Once trapped in organic molecules, that energy is available to both producers and consumers. 1. Cellular Respiration/ Fermentation are energy yielding.

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Chapter 9 Cellular Respiration: Harvesting Chemical Energy

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  1. Chapter 9Cellular Respiration: Harvesting Chemical Energy

  2. Introduction • Energy for work enters as LIGHT • Once trapped in organic molecules, that energy is available to both producers and consumers

  3. 1. Cellular Respiration/ Fermentation are energy yielding Catabolic pathways: Fermentation = no oxygen Cellular Respiration= oxygen • Most of Cellular Respiration occurs in MITOCHONDRIA: Organic compounds + oxygen Carbon dioxide + water + E (ATP+HEAT)

  4. 1. Cellular Respiration/ Fermentation are energy yielding Carbohydrates, Fats, Proteins can all be used for fuel, but glucose is commonly used to learn the process: FORMULA: C6H12O6 + 6O2 ---> 6CO2 + 6H2O + E (ATP + heat)

  5. 2. Cells Recycle ATP for WORK • The price of cellular work is the exergonic reaction which converts ATP→ADP+Pi (inorganic phosphate) • Cells can regenerate ATP from ADP and Pi by the catabolism of organic molecules.

  6. 2. Cells Recycle ATP for WORK

  7. 3.Redox reactions release energy • Oxidation-reduction • OIL RIG (adding e- reduces + charge) • Oxidation is e- loss; reduction is e- gain • Reducing agent: e- donor • Oxidizing agent: e- acceptor

  8. 3. Redox reactions release energy Relocation of e- closer to oxygen releases chemical energy for work! • Why are they so important to understand? • Relocation of electrons releases stored energy • Not all redox reactions completely transfer electrons, some just change degree of sharing in bonds • Electrons release energy as they more from a less electronegative atom to a more electronegative atom

  9. 4. Electrons “Fall” From Organic Compounds to Oxygen during C. Resp Glucose/ Other fuel molecules are oxidized = release of energy Molecules with lots of H atoms, lots of atoms that can be transferred to a more electronegative O RICH RESERVOIR OF Hydrogen ELECTRONS=CARBS, FATS, need ENZYMES TO combine with O2

  10. 5. Fall of Electrons is gradual, via NAD+ and Electron Transport Chain • NAD+ (nicotinamide adenine dinucleotide) • Removes electrons from food (series of reactions) • NAD + is reduced to NADH • Enzyme action: dehydrogenase • Oxygen is the eventual e- acceptor

  11. 5. Fall of Electrons is gradual, via NAD+ and Electron Transport Chain • H- atoms are stripped from glucose, passed to coenzyme: NICOTINAMIDE ADENINE DINUCLEOTIDE • Dehydrogenase enzymes strip two hydrogens from fuel, pass two electrons and one proton to NAD+ and release H+ • THIS MAKES REDUCED FORM= NADH • NADH= Reducing agent, electrons lose very little energy and energy is“tapped” to synthesize ATP as electrons move from NADH to oxygen

  12. 5. “Fall” of Electrons is gradual, via NAD+ and Electron Transport Chain • Electron carrier molecules (membrane proteins) • Shuttles electrons that release energy used to make ATP • Sequence of reactions that prevents energy release in 1 explosive step • Electron route: food---> NADH ---> electron transport chain ---> oxygen

  13. Cellular respiration: an overview • 1. Glycolysis: cytosol; degrades glucose into pyruvate • 2. Kreb’s Cycle: mitochondrial matrix; pyruvate into carbon dioxide • 3.Electron Transport Chain: inner membrane of mitochondrion; electrons passed to oxygen

  14. Cellular respiration: an overview • Several steps in Glycolysis and the Krebs cycle transfer electrons from substrates to NAD+ forming NADH • NADH passes these electrons to the electron transport chain. The electron transport chain moves electrons from molecule to molecule until they combine with O and H ions and form water.

  15. Cellular respiration: an overview MAKING ATP: Substrate-level phosphorylation: The formation of ATP by directly transferring a phosphate group to ADP from intermediate substrate in catabolism. Oxidative Phosphorylation: The production of ATP using energy derived from redox reactions of an electron transport chain

  16. Glycolysis and Cellular Respiration

  17. Glycolysis: oxidation of glucose to pyruvate GLUCOSE to 2 pyruvate molecules 1. Energy investment phase: cell uses 2 ATP to phosphorylate fuel 2. Energy payoff phase: ATP is produced by substrate-level phosphorylation and NAD+ is reduced to NADH by food oxidation

  18. Glycolysis: oxidation of glucose to pyruvate Net energy yield per glucose molecule: 2 ATP plus 2 NADH; no CO2 is released; occurs aerobically or anaerobically Each step in glycolysis is catalyzed by a specific enzyme! If oxygen is present, pyruvate moves to Kreb’s cycle…

  19. Kreb’s Cycle • If molecular oxygen is present……. • Each pyruvate is converted into acetyl CoA (begin w/ 2): 1 A carboxyl group is removed as CO2 2. A pair of electrons is transferred from remaining 2- carbon fragment to NAD+ to form NADH 3. Oxidized fragment acetate, combines with coenzyme A to form acetyl CoA.

  20. Kreb’s Cycle • From this point, each turn 2 C atoms enter (pyruvate) and 2 exit (carbon dioxide) •This cycle begins when acetate from acetyl CoA combines with oxaloacetate to form citrate. •Ultimately, the oxaloacetate is recycled and the acetate is broken down to CO2. • For each pyruvate that enters: • 3 NAD+ reduced to NADH; • 1 FAD+ reduced to FADH2 (riboflavin, B vitamin); • 1 ATP molecule

  21. Kreb’s Cycle • Kreb’s Cycle consists of 8 steps • The conversion of pyruvate and the Kreb’s cycle produces large quantities of ELECTRON CARRIERS

  22. Electron transport chain 1000s of copies of the electron transport chain are found in the extensive surface of the cristae, the inner membrane of the mitochondrion. • THE BEGINNING: • Most components of the chain are proteins that are bound with prosthetic groups: alternate between reduced and oxidized states as they accept and donate electrons. •Electrons drop in free energy as they pass down the electron transport chain. •Electrons carried by NADH are transferred to the first molecule in the electron transport chain, flavoprotein. • The electrons continue along the chain that includes several cytochrome proteins and one lipid carrier.

  23. Electron transport chain • Electrons carried by FADH2 = lower free energy, added to a later point in the chain. • For every two electron carriers (four e), 1 O2 molecule is reduced to 2 molecules of water. • No generation of ATP directly. • Function: break the large free energy drop from food to oxygen into a series of smaller steps • Electrons from NADH or FADH2 ultimately pass to oxygen.

  24. Electron transport chain • The movement of electrons along the electron transport chain does contribute to chemiosmosis and ATP synthesis.

  25. Electron transport chain • ATP synthase, in the cristae, actually makes ATP from ADP and Pi. • ATP uses the energy of proton gradient to power ATP synthesis. • Proton gradient develops between the intermembrane space and the matrix. • The proton gradient is produced by the movement of electrons along the electron transport chain. • •Several chain molecules can use the exergonic flow of electrons to pump H+ from the matrix to the intermembrane space. • •This concentration of H+ is the proton-motive force.

  26. ETC: ATP synthase • ATP synthase molecules: only place that will allow H+ to diffuse back to the matrix. • Exergonic flow of H+ is used by the enzyme to generate ATP. • Coupling of the redox reactions of the electron transport chain to ATP synthesis is called chemiosmosis.

  27. Electron Transport: Making ATP 1. As hydrogen ions flow down their gradient, they cause the cylinder portion and attached rod of ATP synthase to rotate. 2.The spinning rod causes a conformational change in the knob region, activating catalytic sites where ADP and inorganic phosphate combine to make ATP

  28. Review: Cellular Respiration • Glycolysis:2 ATP (substrate-level phosphorylation) • Kreb’s Cycle: 2 ATP (substrate-level phosphorylation) • Electron transport & oxidative phosphorylation: 2 NADH (glycolysis) = 6ATP 2 NADH (acetyl CoA) = 6ATP 6 NADH (Kreb’s) = 18 ATP 2 FADH2 (Kreb’s) = 4 ATP • 38 TOTAL ATP/glucose

  29. Related metabolic processes… •Glycolysis :2 ATP whether oxygen is present or not . •Anaerobic catabolism of sugars: FERMENTATION •Fermentation can generate ATP from glucose by substrate-level phosphorylation as long as there is a supply of NAD+ to accept electrons. •If NAD+ pool is exhausted, glycolysis shuts down. • aerobic conditions: NADH transfers its electrons to the electron transfer chain, recycling NAD+. • anaerobic conditions: various fermentation pathways generate ATP by glycolysis and recycle NAD+ by transferring electrons from NADH to pyruvate or derivatives of pyruvate

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