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Cellular Respiration

Cellular Respiration. Cellular Respiration. Respiration is a cumulative function of three metabolic stages Glycolysis The citric acid cycle (TCA or Krebbs) Oxidative phosphorylation. C 6 H 12 O 6 + 6O 2    <---->   6 CO 2 + 6 H 2 0    + e- --->    36-38 ATP. Respiration. Glycolysis

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Cellular Respiration

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  1. Cellular Respiration

  2. Cellular Respiration • Respiration is a cumulative function of three metabolic stages • Glycolysis • The citric acid cycle (TCA or Krebbs) • Oxidative phosphorylation C6H12O6+ 6O2   <---->   6 CO2+ 6 H20    + e- --->    36-38 ATP

  3. Respiration • Glycolysis • Breaks down glucose into two molecules of pyruvate • The citric acid cycle (Krebs Cycle) • Completes the breakdown of glucose • Oxidative phosphorylation • Is driven by the electron transport chain • Generates ATP

  4. Electrons carried via NADH and FADH2 Electrons carried via NADH Oxidativephosphorylation:electron transport andchemiosmosis Citric acid cycle Glycolsis Pyruvate Glucose Cytosol Mitochondrion ATP ATP ATP Substrate-level phosphorylation Oxidative phosphorylation Substrate-level phosphorylation Figure 9.6 Respiration Overview 2 ATP 2 ATP 32-34 ATP

  5. Enzyme Enzyme ADP P Substrate + ATP Product Figure 9.7 Substrate Level Phosphorylation • Both glycolysis and the citric acid cycle • Can generate ATP by substrate-level phosphorylation

  6. Oxidativephosphorylation Glycolysis Citricacidcycle ATP ATP ATP Energy investment phase Glucose 2 ATP + 2 used 2 ATP P Energy payoff phase formed 4 ATP 4 ADP + 4 P 2 NADH 2 NAD+ + 4 e- + 4 H + + 2 H+ 2 Pyruvate + 2 H2O Glucose 2 Pyruvate + 2 H2O 4 ATP formed – 2 ATP used 2 ATP + 2 H+ 2 NAD+ + 4 e– + 4 H + 2 NADH Figure 9.8 Glycolysis • Harvests energy by oxidizing glucose to pyruvate • Glycolysis • Means “splitting of sugar” • Breaks down glucose into pyruvate • Occurs in the cytoplasm of the cell • Two major phases • Energy investment phase • Energy payoff phase

  7. The First Stage of Glycolysis • Glucose (6C) is broken down into 2 PGAL's (3C) • This requires two ATP's ENERGY INVESTMENT STAGE

  8. The Second Stage of Glycolysis • 2 PGAL's (3C) are converted to 2 pyruvates • This creates 4 ATP's and 2 NADH's • The net ATP production of Glycolysis is 2 ATP's ENERGY PAY-OFF STAGE

  9. Glycolysis Summary

  10. Citric Acid Cyclea.k.a. Krebs Cycle • Completes the energy-yielding oxidation of organic molecules • The citric acid cycle • Takes place in the matrix of the mitochondrion

  11. What is the starting molecule for the Krebs Cycle? Acetyl CoA

  12. If the end product of glycolysis is pyruvate, how can the Krebs cycle start with acetyl CoA? • Pyruvate converts to acetyl CoA as it enters the mitochondrial matrix. What is lost or gained during this process? One carbon atom is lost as CO2 , an electron is given to NADH & a different 2-carbon chain is the result.

  13. Krebs's Cycle (citric acid cycle, TCA cycle) • Goal: take pyruvate and put it into the Krebs's cycle, producing FADH2 and more NADH • Where: the mitochondria matrix • There are two steps • The Conversion of Pyruvate to Acetyl CoA • The Kreb's Cycle proper • In the Krebs's cycle, all of Carbons, Hydrogens, and Oxygen in pyruvate end up as CO2 and H2O • The Krebs's cycle produces 2 ATP's, 6 NADH's, and 2FADH2's per glucose molecule

  14. Fate of Pyruvate

  15. CYTOSOL MITOCHONDRION + H+ NAD+ NADH O– CoA S 2 C O C O C O CH3 1 3 CH3 Acetyle CoA Pyruvate CO2 Coenzyme A Transport protein Figure 9.10 Before the Krebs cycle can begin….we have the link reaction • Pyruvate must first be converted to acetyl CoA, which links the cycle to glycolysis

  16. The Krebs Cycle • 6 NADH's are generated • 2 FADH2 is generated • 2 ATP are generated • 4 CO2's are released Two turns for each molecule of glucose because each glucose is converted to 2 molecules of acetyl CoA.

  17. If the main purpose of cell respiration is to produce ATP, why do glycolysis & the Krebs cycle only make 4 molecules of ATP total by the time glucose has been converted to carbon dioxide? Although glycolysis & the Krebs cycle only produce 4 ATP molecules when glucose is converted to CO2 , these reactions produce 12 shuttle molecules of NADH & FADH2 which eventually generated 90% of the total ATP production during the final phase of cell respiration.

  18. After the Krebs Cycle… • During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis • NADH and FADH2 • Donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation

  19. The Pathway of Electron Transport • In the electron transport chain • Electrons from NADH and FADH2 lose energy in several steps • At the end of the chain • Electrons are passed to oxygen, forming water

  20. ETC • Electron transfer causes protein complexes to pump H+ from the mitochondrial matrix to the intermembrane space • The resulting H+ gradient • Stores energy • Drives chemiosmosis in ATP synthase • Is referred to as a proton-motive force

  21. How does electronegativity play a part in the electron transport chain? Because each electron acceptor in the chain is more electronegative than the previous, the electron will move from one electron transport chain molecule to the next, falling closer and closer to the nucleus of the last electron acceptor. Where do the electrons for the ETC come from? NADH and FADH2 which got theirs from glucose. What molecule is the final acceptor of the electron? Water, from splitting O2 molecule & grabbing 2 H+ . What’s consumed during this process? O2 What’s gained by this process? H+ inside the inner membrane space

  22. Chemiosmosis • Is an energy-coupling mechanism that uses energy in the form of a H+ gradient across a membrane to drive cellular work H+ gradient = Proton motive force

  23. INTERMEMBRANE SPACE A rotor within the membrane spins clockwise whenH+ flows past it down the H+ gradient. H+ H+ H+ H+ H+ H+ H+ A stator anchoredin the membraneholds the knobstationary. A rod (for “stalk”)extending into the knob alsospins, activatingcatalytic sites inthe knob. H+ Three catalytic sites in the stationary knobjoin inorganic Phosphate to ADPto make ATP. ADP + ATP P i MITOCHONDRIAL MATRIX Figure 9.14 Chemiosmosis: The Energy-Coupling Mechanism • ATP synthase • Is the enzyme that actually makes ATP 32-34 ATP

  24. Inner Mitochondrial membrane Oxidative phosphorylation. electron transport and chemiosmosis Glycolysis ATP ATP ATP H+ H+ H+ H+ Cyt c Protein complex of electron carners Intermembrane space Q IV I III ATP synthase Inner mitochondrial membrane II H2O FADH2 2 H+ + 1/2 O2 FAD+ NADH+ NAD+ ATP ADP + P i (Carrying electrons from, food) H+ Mitochondrial matrix Chemiosmosis ATP synthesis powered by the flow Of H+ back across the membrane Electron transport chain Electron transport and pumping of protons (H+), which create an H+ gradient across the membrane Figure 9.15 Oxidative phosphorylation

  25. An Accounting of ATP Production by Cellular Respiration • During respiration, most energy flows in this sequence • Glucose to NADH to electron transport chain to proton-motive force to ATP

  26. Net Energy Production from Aerobic Respiration • Glycolysis: 2 ATP • Kreb's Cycle: 2 ATP • Electron Transport Phosphorylation: 32-34 ATP • Each NADH produced in Glycolysis is worth 2 ATP (2 x 2 = 4) - the NADH is worth 3 ATP, but it costs an ATP to transport the NADH into the mitochondria, so there is a net gain of 2 ATP for each NADH produced in gylcolysis • Each NADH produced in the conversion of pyruvate to acetyl COA and Kreb's Cycle is worth 3 ATP (8 x 3 = 24) • Each FADH2 is worth 2 ATP (2 x 2 = 4) • 4 + 24 + 4 = 32 • Net Energy Production: 36-38 ATP

  27. Is cellular respiration endergonic or exergonic? exergonic Is it a catabolic or anabolic process? catabolic • If one ATP molecule holds 7.3kcal of potential energy, how much potential energy does 1 glucose molecule produce in cell respiration? • One molecule of glucose actually contains 686 kcal/mol of potential energy. Where does the remaining energy go when glucose is reduced? • What is the net efficiency of cell respiration if glucose contains 686kcal and only 277.4kcal are produced? At its maximum output, 38 x 7.3kcal = 277.4kcal It’s lost as heat-which is why our bodies are warm right now. • 277.4/ 686 x 100 = 40% energy recovered from aerobic respiration

  28. Is 40% net efficiency of cellular respiration good or not? • Let’s first look at the following energy capturing processes that you see in everyday life. An incandescent light bulb is about 5% efficient Electricity generated from coal is about 21% efficient The most efficient gasoline combustion engine in cars is about 23% efficient. So…now what do you think?

  29. Electron shuttles span membrane MITOCHONDRION CYTOSOL 2 NADH or 2 FADH2 2 FADH2 2 NADH 2 NADH 6 NADH Glycolysis Oxidative phosphorylation: electron transport and chemiosmosis Citric acid cycle 2 Acetyl CoA 2 Pyruvate Glucose + 2 ATP + 2 ATP + about 32 or 34 ATP by substrate-level phosphorylation by substrate-level phosphorylation by oxidative phosphorylation, depending on which shuttle transports electrons from NADH in cytosol About 36 - 38 ATP Maximum per glucose: Figure 9.16

  30. OCCURS IN CYTOSOL OCCURS IN MITOCHONDRIA OCCURS IN CYTOSOL

  31. Anaerobic Respiration • Fermentation enables some cells to produce ATP without the use of oxygen • Glycolysis • Can produce ATP with or without oxygen, in aerobic or anaerobic conditions • Couples with fermentation to produce ATP

  32. Anaerobic Respiration • Fermentation consists of • Glycolysis plus reactions that regenerate NAD+, which can be reused by glyocolysis • Alcohol fermentation • Pyruvate is converted to ethanol in two steps, one of which releases CO2 • Lactic acid fermentation • Pyruvate is reduced directly to NADH to form lactate as a waste product

  33. P1 2 ATP 2 ADP + 2 O – C O C O Glucose Glycolysis CH3 2 Pyruvate 2 NADH 2 NAD+ 2 CO2 H H H C C O OH CH3 CH3 2 Ethanol 2 Acetaldehyde (a) Alcohol fermentation P1 2 ATP 2 ADP + 2 Glucose Glycolysis O– C O C O 2 NADH 2 NAD+ CH3 O C O H OH C CH3 2 Lactate (b) Lactic acid fermentation Figure 9.17

  34. Glucose CYTOSOL Pyruvate No O2 present Fermentation O2 present Cellular respiration MITOCHONDRION Ethanol or lactate Acetyl CoA Citric acid cycle Figure 9.18 Pyruvate is a key juncture in catabolism

  35. Glycolysis • Occurs in nearly all organisms • Probably evolved in ancient prokaryotes before there was oxygen in the atmosphere

  36. Glucose AMP Glycolysis Stimulates Fructose-6-phosphate + Phosphofructokinase – – Fructose-1,6-bisphosphate Inhibits Inhibits Pyruvate Citrate ATP Acetyl CoA Citric acid cycle Oxidative phosphorylation Figure 9.20 • Cellular respiration • Is controlled by allosteric enzymes at key points in glycolysis and the citric acid cycle Feedback inhibition

  37. Fats Carbohydrates Proteins Sugars Amino acids Fatty acids Glycerol Glycolysis Glucose Glyceraldehyde-3- P NH3 Pyruvate Acetyl CoA Citric acid cycle Oxidative phosphorylation Figure 9.19

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