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LE 8-8

LE 8-8. Adenine. Phosphate groups. Ribose. Using Hydrolysis to break the phosphate bond. LE 8-9. P. P. P. Adenosine triphosphate (ATP). H 2 O. +. P. P. P. +. Energy. i. Adenosine diphosphate (ADP). Inorganic phosphate. How ATP Performs Work.

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LE 8-8

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  1. LE 8-8 Adenine Phosphate groups Ribose

  2. Using Hydrolysis to break the phosphate bond

  3. LE 8-9 P P P Adenosine triphosphate (ATP) H2O + P P P + Energy i Adenosine diphosphate (ADP) Inorganic phosphate

  4. How ATP Performs Work • ATP drives endergonic reactions by phosphorylation, transferring a phosphate group to some other molecule, such as a reactant • The recipient molecule is now phosphorylated • The three types of cellular work (mechanical, transport, and chemical) are powered by the hydrolysis of ATP

  5. P i P LE 8-11 Protein moved Motor protein Mechanical work: ATP phosphorylates motor proteins Membrane protein ADP ATP + P i P P i Solute transported Solute Transport work: ATP phosphorylates transport proteins P NH2 NH3 P + + Glu i Glu Reactants: Glutamic acid and ammonia Product (glutamine) made Chemical work: ATP phosphorylates key reactants

  6. Light energy LE 9-2 ECOSYSTEM Photosynthesis in chloroplasts Organic molecules CO2 + H2O + O2 Cellular respiration in mitochondria ATP powers most cellular work Heat energy

  7. Several processes are central to cellular respiration and related pathways

  8. Production of ATP • The breakdown of organic molecules is exergonic • Fermentation is a partial degradation of sugars that occurs without oxygen • Cellular respiration consumes oxygen and organic molecules and yields ATP • Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration with the sugar glucose: C6H12O6 + 6O2 6CO2 + 6H2O + Energy (ATP + heat)

  9. The transfer of electrons during chemical reactions releases energy stored in organic molecules • This released energy is ultimately used to synthesize ATP

  10. becomes oxidized C6H12O6 + 6O2 6CO2 + 6H2O + Energy becomes reduced • During cellular respiration, the fuel (such as glucose) is oxidized and oxygen is reduced:

  11. the Electron Transport Chain • In cellular respiration, glucose and other organic molecules are broken down in a series of steps • Electrons from organic compounds are usually first transferred to NAD+, a coenzyme • As an electron acceptor, NAD+ functions as an oxidizing agent during cellular respiration • Each NADH (the reduced form of NAD+) represents stored energy that is tapped to synthesize ATP

  12. NADH passes the electrons to the electron transport chain • Unlike an uncontrolled reaction, the electron transport chain passes electrons in a series of steps instead of one explosive reaction • Oxygen pulls electrons down the chain in an energy-yielding tumble • The energy yielded is used to regenerate ATP

  13. H2 1/2 O2 + + 1/2 O2 2 H (from food via NADH) LE 9-5 Controlled release of energy for synthesis of ATP 2 H+ + 2 e– ATP Explosive release of heat and light energy ATP Free energy, G Free energy, G ATP Electron transport chain 2 e– 1/2 O2 2 H+ H2O H2O Uncontrolled reaction Cellular respiration

  14. The Stages of Cellular Respiration: A Preview • Cellular respiration has three stages: • Glycolysis (breaks down glucose into two molecules of pyruvate) • Kreb’s cycle • Electron Transport System • The process that generates most of the ATP is called oxidative phosphorylation because it is powered by redox reactions

  15. LE 9-6_1 Glycolysis Pyruvate Glucose Cytosol Mitochondrion ATP Substrate-level phosphorylation

  16. LE 9-6_2 Glycolysis Kreb’s Cycle Pyruvate Glucose Cytosol Mitochondrion ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation

  17. LE 9-6_3 Electrons carried via NADH and FADH2 Electrons carried via NADH Oxidative phosphorylation: electron transport and chemiosmosis Glycolysis Krebs cycle Pyruvate Glucose Cytosol Mitochondrion ATP ATP ATP Substrate-level phosphorylation Oxidative phosphorylation Substrate-level phosphorylation

  18. Oxidative phosphorylation accounts for almost 90% of the ATP generated by cellular respiration (electron transport system) • A small amount of ATP is formed in glycolysis and the Krebs cycle

  19. Glycolysis harvests energy by oxidizing glucose to pyruvate • Glycolysis (“splitting of sugar”) breaks down glucose into two molecules of pyruvate • Glycolysis occurs in the cytoplasm and has two major phases: • Energy investment phase • Energy payoff phase

  20. Energy investment phase LE 9-8 Glucose 2 ATP 2 ADP + 2 P used Citric acid cycle Glycolysis Oxidative phosphorylation Energy payoff phase formed ATP ATP ATP 4 ADP + 4 P 4 ATP 2 NADH + 2 H+ 2 NAD+ + 4 e– + 4 H+ 2 Pyruvate + 2 H2O Net 2 Pyruvate + 2 H2O Glucose 4 ATP formed – 2 ATP used 2 ATP 2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+

  21. Citric acid cycle Glycolysis Oxidation phosphorylation ATP ATP ATP Glucose LE 9-9a_1 ATP Hexokinase ADP Glucose-6-phosphate

  22. Citric acid cycle Glycolysis Oxidation phosphorylation ATP ATP ATP Glucose LE 9-9a_2 ATP Hexokinase ADP Glucose-6-phosphate Phosphoglucoisomerase Fructose-6-phosphate ATP Phosphofructokinase ADP Fructose- 1, 6-bisphosphate Aldolase Isomerase Dihydroxyacetone phosphate Glyceraldehyde- 3-phosphate

  23. 2 NAD+ Triose phosphate dehydrogenase NADH 2 + 2 H+ LE 9-9b_1 1, 3-Bisphosphoglycerate 2 ADP Phosphoglycerokinase 2 ATP 3-Phosphoglycerate Phosphoglyceromutase 2-Phosphoglycerate

  24. 2 NAD+ Triose phosphate dehydrogenase NADH 2 + 2 H+ LE 9-9b_2 1, 3-Bisphosphoglycerate 2 ADP Phosphoglycerokinase 2 ATP 3-Phosphoglycerate Phosphoglyceromutase 2-Phosphoglycerate Enolase 2 H2O Phosphoenolpyruvate 2 ADP Pyruvate kinase 2 ATP Pyruvate

  25. The Krebs cycle completes the energy-yielding oxidation of organic molecules • Before the Krebs cycle can begin, pyruvate must be converted to acetyl CoA, which links the cycle to glycolysis

  26. LE 9-10 MITOCHONDRION CYTOSOL NAD+ NADH + H+ Acetyl Co A CO2 Coenzyme A Pyruvate Transport protein

  27. The Krebs cycle, takes place within the mitochondrial matrix • The cycle oxidizes organic fuel derived from pyruvate, generating one ATP, 3 NADH, and 1 FADH2 per turn

  28. Pyruvate (from glycolysis, 2 molecules per glucose) Citric acid cycle Glycolysis Oxidation phosphorylation CO2 NAD+ LE 9-11 CoA NADH ATP ATP ATP + H+ Acetyl CoA CoA CoA Krebs cycle 2 CO2 FADH2 3 NAD+ 3 NADH FAD + 3 H+ ADP + P i ATP

  29. The NADH and FADH2 produced by the cycle relay electrons extracted from food to the electron transport chain

  30. Following glycolysis and the Krebs cycle, NADH and FADH2 account for most of the energy extracted from food • These two electron carriers donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation

  31. The Pathway of Electron Transport • The electron transport chain is in the cristae of the mitochondrion • Most of the chain’s components are proteins, which exist in multiprotein complexes • The carriers alternate reduced and oxidized states as they accept and donate electrons • Electrons drop in free energy as they go down the chain and are finally passed to O2, forming water

  32. The electron transport chain generates no ATP • The chain’s function is to break the large free-energy drop from food to O2 into smaller steps that release energy in manageable amounts

  33. Chemiosmosis: The Energy-Coupling Mechanism • Electron transfer in the electron transport chain causes proteins to pump H+ from the mitochondrial matrix to the intermembrane space • H+ then moves back across the membrane, passing through channels in ATP synthase • ATP synthase uses the flow of H+ to drive phosphorylation of ATP • This is an example of chemiosmosis, the use of energy in a H+ gradient to drive cellular work

  34. INTERMEMBRANE SPACE A rotor within the membrane spins as shown when H+ flows past it down the H+ gradient. H+ H+ H+ LE 9-14 H+ H+ H+ H+ A stator anchored in the membrane holds the knob stationary. A rod (or “stalk”) extending into the knob also spins, activating catalytic sites in the knob. H+ Three catalytic sites in the stationary knob join inorganic phosphate to ADP to make ATP. ADP + ATP P i MITOCHONDRAL MATRIX

  35. Inner mitochondrial membrane LE 9-15 Oxidative phosphorylation: electron transport and chemiosmosis Citric acid cycle Glycolysis ATP ATP ATP H+ H+ H+ H+ Cyt c Protein complex of electron carriers Intermembrane space Q IV III I ATP synthase II Inner mitochondrial membrane H2O 2H+ + 1/2 O2 FADH2 FAD NAD+ NADH + H+ ATP ADP + P i (carrying electrons from food) H+ Mitochondrial matrix Electron transport chain Electron transport and pumping of protons (H+), Which create an H+ gradient across the membrane Chemiosmosis ATP synthesis powered by the flow of H+ back across the membrane Oxidative phosphorylation

  36. An Accounting of ATP Production by Cellular Respiration • During cellular respiration, most energy flows in this sequence: glucose NADH electron transport chain proton-motive force ATP • About 40% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about 38 ATP

  37. Electron shuttles span membrane LE 9-16 MITOCHONDRION CYTOSOL 2 NADH or 2 FADH2 2 NADH 2 NADH 6 NADH 2 FADH2 Oxidative phosphorylation: electron transport and chemiosmosis Glycolysis 2 Acetyl CoA Citric acid cycle 2 Pyruvate Glucose + 2 ATP + 2 ATP + about 32 or 34 ATP by substrate-level phosphorylation by substrate-level phosphorylation by oxidation phosphorylation, depending on which shuttle transports electrons form NADH in cytosol About 36 or 38 ATP Maximum per glucose:

  38. Fermentation enables some cells to produce ATP without the use of oxygen • Cellular respiration requires O2 to produce ATP • Glycolysis can produce ATP with or without O2 (in aerobic or anaerobic conditions) • In the absence of O2, glycolysis couples with fermentation to produce ATP

  39. Types of Fermentation • Fermentation consists of glycolysis plus reactions that regenerate NAD+, which can be reused by glycolysis • Two common types are alcohol fermentation and lactic acid fermentation

  40. In alcohol fermentation, pyruvate is converted to ethanol in two steps, with the first releasing CO2 • Alcohol fermentation by yeast is used in brewing, winemaking, and baking

  41. P 2 ADP + 2 2 ATP i LE 9-17a Glycolysis Glucose 2 Pyruvate 2 NAD+ 2 NADH CO2 2 + 2 H+ 2 Acetaldehyde 2 Ethanol Alcohol fermentation

  42. In lactic acid fermentation, pyruvate is reduced to NADH, forming lactate as an end product, with no release of CO2 • Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt • Human muscle cells use lactic acid fermentation to generate ATP when O2 is scarce

  43. P 2 ADP + 2 2 ATP i LE 9-17b Glycolysis Glucose 2 NAD+ 2 NADH CO2 2 + 2 H+ 2 Pyruvate 2 Lactate Lactic acid fermentation

  44. Fermentation and Cellular Respiration Compared • Both processes use glycolysis to oxidize glucose and other organic fuels to pyruvate • The processes have different final electron acceptors: an organic molecule (such as pyruvate) in fermentation and O2 in cellular respiration • Cellular respiration produces much more ATP

  45. Glucose CYTOSOL LE 9-18 Pyruvate O2 present Cellular respiration No O2 present Fermentation MITOCHONDRION Acetyl CoA Ethanol or lactate Citric acid cycle

  46. Concept 9.6: Glycolysis and the citric acid cycle connect to many other metabolic pathways • Gycolysis and the Krebs cycle are major intersections to various catabolic and anabolic pathways

  47. The Versatility of Catabolism • Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration • Glycolysis accepts a wide range of carbohydrates • Proteins must be digested to amino acids; amino groups can feed glycolysis or the citric acid cycle • Fats are digested to glycerol (used in glycolysis) and fatty acids (used in generating acetyl CoA) • An oxidized gram of fat produces more than twice as much ATP as an oxidized gram of carbohydrate

  48. Proteins Carbohydrates Fats Amino acids Sugars Glycerol Fatty acids LE 9-19 Glycolysis Glucose Glyceraldehyde-3- P NH3 Pyruvate Acetyl CoA Citric acid cycle Oxidative phosphorylation

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