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Chapter 8

Figure 8.1. Chapter 8. Overview: The Energy of Life The living cell Is a miniature factory where thousands of reactions occur Converts energy in many ways. Metabolism Is the totality of an organism’s chemical reactions Arises from interactions between molecules.

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Chapter 8

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  1. Figure 8.1 Chapter 8 • Overview: The Energy of Life • The living cell • Is a miniature factory where thousands of reactions occur • Converts energy in many ways

  2. Metabolism • Is the totality of an organism’s chemical reactions • Arises from interactions between molecules Metabolism= Catabolism + Anabolism

  3. More free energy (higher G) • Less stable • Greater work capacity • In a spontaneously change • The free energy of the system decreases (∆G<0) • The system becomes more stable • The released free energy can • be harnessed to do work . • Less free energy (lower G) • More stable • Less work capacity (a) Gravitational motion. Objects move spontaneously from a higher altitude to a lower one. (c) (b) Diffusion. Molecules in a drop of dye diffuse until they are randomly dispersed. Chemical reaction. In a cell, a sugar molecule is broken down into simpler molecules. Figure 8.5  • At maximum stability • The system is at equilibrium Not Stable Yeah! More STABLE

  4. ∆G < 0 ∆G < 0 ∆G < 0 (c) A multistep open hydroelectric system. Cellular respiration is analogous to this system: Glucose is broken down in a series of exergonic reactions that power the work of the cell. The product of each reaction becomes the reactant for the next, so no reaction reaches equilibrium. Figure 8.7 • An analogy for cellular respiration Not stable Stable

  5. Adenine NH2 C N C N HC O O O CH C N - N O O O O CH2 O - - - O O O H H Phosphate groups H H Ribose Figure 8.8 OH OH The Structure and Hydrolysis of ATP • ATP (adenosine triphosphate) • Is the cell’s energy shuttle • Provides energy for cellular functions

  6. P P P Adenosine triphosphate (ATP) H2O Energy + P i P P Adenosine diphosphate (ADP) Inorganic phosphate Figure 8.9 • Energy is released from ATP • When the terminal phosphate bond is broken

  7. Endergonic reaction: ∆G is positive, reaction is not spontaneous NH2 NH3 + ∆G = +3.4 kcal/mol Glu Glu Glutamine Glutamic acid Ammonia Exergonic reaction: ∆ G is negative, reaction is spontaneous ∆G = + 7.3 kcal/mol + P ADP H2O ATP + Coupled reactions: Overall ∆G is negative; together, reactions are spontaneous ∆G = –3.9 kcal/mol Figure 8.10 • ATP hydrolysis • Can be coupled to other reactions

  8. P i P Motor protein Protein moved (a) Mechanical work: ATP phosphorylates motor proteins Membrane protein ADP + ATP P i P P i Solute Solute transported (b) Transport work: ATP phosphorylates transport proteins P NH2 + + NH3 P i Glu Glu Reactants: Glutamic acid and ammonia Product (glutamine) made Figure 8.11 (c) Chemical work: ATP phosphorylates key reactants • The three types of cellular work • Are powered by the hydrolysis of ATP

  9. Enzyme 1 Enzyme 2 Enzyme 3 A D C B Reaction 1 Reaction 2 Reaction 3 Startingmolecule Product Organization of the Chemistry of Life into Metabolic Pathways • A metabolic pathway has many steps • That begin with a specific molecule and end with a product • That are each catalyzed by a specific enzyme

  10. Catabolic pathways • Break down complex molecules into simpler compounds • Exergonic reaction - Release energy

  11. Anabolic pathways • Build complicated molecules from simpler ones • Consume energy

  12. Forms of Energy • Energy • Is the capacity to cause change • Exists in various forms, of which some can perform work

  13. Kinetic energy • Is the energy associated with motion • Potential energy • Is stored in the location of matter • Includes chemical energy stored in molecular structure

  14. Chapter 9 Cellular Respiration: Harvesting Chemical Energy

  15. Overview: Life Is Work • Living cells • Require transfusions of energy from outside sources to perform their many tasks

  16. Figure 9.1 • The giant panda • Obtains energy for its cells by eating plants

  17. Light energy ECOSYSTEM Photosynthesisin chloroplasts Organicmolecules CO2 + H2O + O2 Cellular respirationin mitochondria ATP powers most cellular work Heatenergy Figure 9.2 • Energy • Flows into an ecosystem as sunlight and leaves as heat

  18. Concept 9.1: Catabolic pathways yield energy by oxidizing organic fuels

  19. Catabolic Pathways and Production of ATP • The breakdown of organic molecules is exergonic- releases energy

  20. One catabolic process, fermentation • Is a partial degradation of sugars that occurs without oxygen

  21. Cellular respiration • Is the most prevalent and efficient catabolic pathway • Consumes oxygen and organic molecules such as glucose • Yields ATP

  22. Redox Reactions: Oxidation and Reduction • Catabolic pathways yield energy • Due to the transfer of electrons from high potential energy (i.e. in animal cell from Glucose) to • Low potential energy (electron acceptor usually an electron carrier, but ultimately delivered to oxygen in the mitochondria)

  23. The Principle of Redox • Redox reactions • Transfer electrons from one reactant to another by oxidation and reduction

  24. In oxidation • A substance loses electrons, or is oxidized • In reduction • A substance gains electrons, or is reduced

  25. becomes oxidized(loses electron) Na + Cl Na+ + Cl– becomes reduced(gains electron) • Examples of redox reactions

  26. becomes oxidized C6H12O6 + 6O2 6CO2 + 6H2O + Energy becomes reduced Oxidation of Organic Fuel Molecules During Cellular Respiration • During cellular respiration • Glucose is oxidized and oxygen is reduced

  27. Stepwise Energy Harvest via NAD+ and the Electron Transport Chain • Cellular respiration • Oxidizes glucose in a series of steps

  28. 2 e– + 2 H+ 2 e– + H+ NAD+ NADH H Dehydrogenase O O H H Reduction of NAD+ + + 2[H] C NH2 NH2 C (from food) Oxidation of NADH N N+ Nicotinamide(reduced form) Nicotinamide(oxidized form) CH2 O O O O– P O H H OH O O– HO P NH2 HO CH2 O N N H N H N O H H HO OH Figure 9.4 • Electrons from organic compounds • Are usually first transferred to NAD+, a coenzyme- electron carrier

  29. NADH, the reduced form of NAD+ • Passes the electrons to the electron transport chain or system (ETC also known as the ETS) in the Mitochondria Intermembrane space MATRIX

  30. H2 + 1/2 O2 Explosiverelease ofheat and lightenergy (a) Uncontrolled reaction Free energy, G Figure 9.5 A H2O • If electron transfer is not stepwise • A large release of energy occurs • As in the reaction of hydrogen and oxygen to form water

  31. 2 H + 1/2 O2 (from food via NADH) Controlled release of energy for synthesis ofATP 2 H+ + 2 e– ATP ATP Free energy, G Electron transport chain ATP 2 e– 1/2 O2 2 H+ H2O Figure 9.5 B (b) Cellular respiration

  32. The Stages of Cellular Respiration: A Preview • Respiration is a cumulative function of three metabolic stages • Glycolysis • The citric acid cycle • Oxidative phosphorylation

  33. Glycolysis • Breaks down glucose into two molecules of pyruvate • The citric acid cycle • Completes the breakdown of glucose

  34. Oxidative phosphorylation • Is driven by the electron transport chain that occurs in the Mitochondria • Generates ATP

  35. A animal cell

  36. Mitochondrion Intermembrane space Outer membrane Free ribosomes in the mitochondrial matrix Inner membrane Cristae Matrix Mitochondrial DNA 100 µm • Mitochondria are enclosed by two membranes • A smooth outer membrane • An inner membrane folded into cristae Figure 6.17

  37. 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 • An overview of cellular respiration

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

  39. Concept 9.2: 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

  40. Glycolysis Oxidativephosphorylation Citricacidcycle ATP ATP ATP Energy investment phase Glucose P 2 ATP + 2 used 2 ATP Energy payoff phase formed P 4 ATP 4 ADP + 4 2 NAD+ + 4 e- + 4 H + + 2 H+ 2 NADH 2 Pyruvate + 2 H2O Glucose 2 Pyruvate + 2 H2O 4 ATP formed – 2 ATP used 2 ATP + 2 H+ 2 NADH 2 NAD+ + 4 e– + 4 H + Figure 9.8 • Glycolysis consists of two major phases • Energy investment phase • Energy payoff phase

  41. A closer look at the

  42. CH2OH Citric acid cycle H H Oxidative phosphorylation H Glycolysis H HO HO OH H OH Glucose 1 2 3 5 4 ATP Hexokinase ADP CH2OH P O H H H H OH HO H OH Glucose-6-phosphate Phosphoglucoisomerase CH2O P O CH2OH H HO HO H H HO Fructose-6-phosphate ATP Phosphofructokinase ADP CH2 O O CH2 P P O HO H OH H HO Fructose- 1, 6-bisphosphate Aldolase H O CH2 P Isomerase C O O C CHOH CH2OH O CH2 P Dihydroxyacetone phosphate Glyceraldehyde- 3-phosphate Figure 9.9 A energy investment phase

  43. 2 NAD+ Triose phosphate dehydrogenase 2 P i 2 NADH + 2 H+ 8 10 7 9 6 2 O C O P CHOH P CH2 O 1, 3-Bisphosphoglycerate 2 ADP Phosphoglycerokinase 2 ATP O– 2 C CHOH O P CH2 3-Phosphoglycerate Phosphoglyceromutase O– 2 C O P C H O CH2OH 2-Phosphoglycerate Enolase 2 H2O O– 2 C O P C O CH2 Phosphoenolpyruvate 2 ADP Pyruvate kinase 2 ATP O– 2 C O C O CH3 Figure 9.8 B Pyruvate payoff phase

  44. Concept 9.3: The citric acid cycle completes the energy-yielding oxidation of organic molecules • The citric acid cycle • Takes place in the matrix of the mitochondrion

  45. 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 citric acid cycle can begin • Pyruvate must first be converted to acetyl CoA, which links the cycle to glycolysis

  46. Pyruvate(from glycolysis,2 molecules per glucose) Oxidativephosphorylation Glycolysis Citricacidcycle ATP ATP ATP CO2 CoA NADH + 3 H+ Acetyle CoA CoA CoA Citricacidcycle 2 CO2 3 NAD+ FADH2 FAD 3 NADH + 3 H+ ADP + Pi ATP Figure 9.11 • An overview of the citric acid cycle

  47. Citric acid cycle Oxidative phosphorylation Glycolysis S CoA C O CH3 Acetyl CoA CoA SH H2O O C COO– NADH 1 COO– CH2 + H+ COO– CH2 COO– NAD+ Oxaloacetate 8 C COO– HO CH2 2 CH2 HC COO– COO– COO– HO CH HO CH Malate Citrate COO– CH2 Isocitrate COO– CO2 Citric acid cycle 3 H2O 7 NAD+ COO– NADH COO– CH + H+ Fumarate CH2 CoA SH HC a-Ketoglutarate CH2 COO– C O 4 6 SH CoA COO– COO– COO– CH2 5 CH2 FADH2 CO2 CH2 CH2 NAD+ FAD C O COO– Succinate NADH CoA P i S + H+ Succinyl CoA GDP GTP ADP ATP Figure 9.12 Citric Acid cycle Figure 9.12

  48. Concept 9.4: 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

  49. The Pathway of Electron Transport • In the electron transport chain • Electrons from NADH and FADH2 lose energy in several steps

  50. NADH 50 FADH2 Multiproteincomplexes I 40 FAD FMN II Fe•S Fe•S O III Cyt b 30 Fe•S Cyt c1 IV Free energy (G) relative to O2 (kcl/mol) Cyt c Cyt a Cyt a3 20 10 0 O2 2 H + + 12 Figure 9.13 H2O • At the end of the chain • Electrons are passed to oxygen, forming water

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