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The Energy of Life: Overview of Metabolism and Cellular Respiration

Explore the intricate processes of metabolism and cellular respiration in living cells, understanding energy conversion, stability, and work capacity. Learn how ATP powers cellular functions and the significance of redox reactions.

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The Energy of Life: Overview of Metabolism and Cellular Respiration

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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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