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Capturing and Releasing Energy

Capturing and Releasing Energy. Chapter 5. 5.1 Impacts/Issues Green Energy. We and most other organisms sustain ourselves by extracting energy stored in the organic products of photosynthesis Photosynthesis

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Capturing and Releasing Energy

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  1. Capturing and Releasing Energy Chapter 5

  2. 5.1 Impacts/IssuesGreen Energy • We and most other organisms sustain ourselves by extracting energy stored in the organic products of photosynthesis • Photosynthesis • Metabolic pathway by which photoautotrophs capture light energy and use it to make sugars from CO2 and water

  3. Biofuels

  4. Green Energy • Autotroph • Organism that makes its own food using carbon from inorganic sources, such as CO2, and energy from the environment • Heterotroph • Organism that obtains energy and carbon from organic compounds assembled by other organisms

  5. Green Energy • Current biofuel research focuses on ways to break down abundant cellulose in fast growing weeds and agricultural wastes

  6. Solar power

  7. 5.2 Capturing Rainbows • Energy radiating from the sun travels through space in waves and is organized in packets called photons • The spectrum of radiant energy from the sun includes visible light

  8. Capturing Rainbows • Humans perceive different wavelengths of visible light as different colors • The shorter the wavelength, the greater the energy • Wavelength • Distance between the crests of two successive waves of light

  9. Capturing Rainbows • Photosynthetic species use pigments to harvest light energy for photosynthesis • Pigment • An organic molecule that can absorb light at specific wavelengths • Chlorophyll a • Main photosynthetic pigment in plants

  10. Wavelength and theElectromagnetic Spectrum

  11. Some Photosynthetic Pigments

  12. 5.3 Storing Energy in Carbohydrates • Photosynthesis converts the energy of light into the energy of chemical bonds, which can power reactions of life and be stored for later use • Photosynthesis takes place in two stages • Light-dependent reactions • Light-independent reactions

  13. The First Stage of Photosynthesis • Light-dependent reactions (“photo”) • Convert light energy to chemical energy of ATP and NADPH, releasing oxygen • Occur at the thylakoid membrane in plant chloroplasts • Photosystem • Cluster of pigments and proteins that converts light energy to chemical energy in photosynthesis

  14. Chloroplasts and the Thylakoid Membrane • Chloroplast • Organelle of photosynthesis in plants and some protists • Thylakoid membrane • Chloroplast’s highly folded inner membrane system • Forms a continuous compartment in the stroma

  15. The Second Stage of Photosynthesis • Light-independent reactions (“synthesis”) • ATP and NADPH drive synthesis of glucose and other carbohydrates from water and CO2 • Occurs in the stroma • Stroma • Semifluid matrix between the thylakoid membrane and the two outer membranes of a chloroplast

  16. A Many photosynthetic cells in a leaf B Many chloroplasts in a photosynthetic cell A Leaf: Sites of Photosynthesis C Many thylakoids in a chloroplast Fig. 5-3, p. 83

  17. Sites of photosynthesis “green spots” are chloroplast

  18. Summary: Photosynthesis 6CO2 + 6H2O → (light energy) → C6 H12O6 + 6O2 A Chloroplast

  19. light water carbon dioxide, water NADPH, ATP light-dependent reactions light- independent reactions NADP+, ADP oxygen glucose Stepped Art Fig. 5-4, p. 84

  20. Chemical bookkeeping

  21. 5.4 The Light-Dependent Reactions • Chlorophylls and other pigments in the thylakoid membrane absorb light energy and pass it to photosystems, which then release electrons • Energized electrons leave photosystems and enter electron transfer chains in the membrane; hydrogen ion gradients drive ATP formation • Oxygen is released; electrons end up in NADPH

  22. Light-Dependent Reactions

  23. Steps in Light-Dependent Reactions 1. Light energy ejects electrons from a photosystem 2. Photosystem pulls replacement electrons from water, releasing O2 3. Electrons enter an electron transfer chain (ETC) in the thylakoid membrane 4. Electron energy is used to form a hydrogen-ion gradient across the thylakoid membrane

  24. Steps in Light-Dependent Reactions 5. Another photosystem receives electrons from the ETC 6. Electrons move through a second ETC; NADPH is formed 7. Hydrogen ions flow across the thylakoid membrane through ATP synthase and power ATP formation in the stroma

  25. Electron Transfer Phosphorylation • Electron transfer phosphorylation • Metabolic pathway in which electron flow through electron transfer chains sets up a hydrogen ion gradient that drives ATP formation

  26. Light-Dependent Reactions to light-independent reactions light energy light energy 4 7 5 1 stroma 3 6 2 thylakoid compartment thylakoid membrane The Light-Dependent Reactions of Photosynthesis Fig. 5-5, p. 85

  27. 5.5 The Light-Independent Reactions • Driven by the energy of ATP and electrons from NADPH, light-independent reactions use carbon and oxygen from CO2 to build sugars

  28. Carbon Fixation • In the stroma of chloroplasts, the enzyme rubisco fixes carbon from CO2 in the Calvin–Benson cycle • Carbon fixation • Process by which carbon from an inorganic source such as CO2 becomes incorporated into an organic molecule

  29. Calvin-Benson Cycle • Calvin-Benson cycle • Light-independent reactions of photosynthesis • Cyclic pathway that forms glucose from CO2 • Uses energy from ATP and electrons from NADPH • Rubisco • Enzyme that fixes carbon from CO2 to RuBP in the Calvin-Benson cycle

  30. Light-Independent Reactions chloroplast CO2, H2O stroma PGA RuBP Calvin– Benson Cycle ATP ATP NADPH sugars Fig. 5-6, p. 86

  31. Calvin-Benson cycle

  32. Carbon-Fixing Adaptations • Several adaptations, such as a waterproof cuticle, allow plants to live where water is scarce • Stomata • Gaps that open between guard cells on plant surfaces; allow gas exchange through the cuticle • C3 plants • Use only the Calvin-Benson cycle to fix carbon • Conserve water by closing stomata on dry days

  33. Photorespiration • When stomata are closed, oxygen builds up and interferes with sugar production • Photorespiration • Reaction in which rubisco attaches O2 instead of CO2 to RuBP

  34. Fig. 5-7d, p. 87

  35. 5.6 Photosynthesis and Aerobic Respiration: A Global Connection • Earth’s atmosphere was permanently altered by the evolution of photosynthesis

  36. Oxygen and the Atmosphere • Photoautotroph • Photosynthetic autotroph • Anaerobic • Occurring in the absence of oxygen • Aerobic • Involving or occurring in the presence of oxygen

  37. Extracting Energy From Carbohydrates • Eukaryotic cells typically convert chemical energy of carbohydrates to chemical energy of ATP by oxygen-requiring aerobic respiration • Aerobic respiration • Aerobic pathway that breaks down carbohydrates to produce ATP • Pathway finishes in mitochondria

  38. Photosynthesis and Aerobic Respiration

  39. An Overview of Aerobic Respiration • Aerobic respiration is divided into three steps 1. Glycolysis 2. Acetyl CoA formation and the Krebs cycle 3. Electron transfer phosphorylation • In the first two stages, coenzymes pick up electrons • In the third stage, electron energy drives ATP synthesis

  40. Aerobic Respiration Begins • Glycolysis • Reactions in which glucose or another sugar is broken down into 2 pyruvates, netting 2 ATP • Pyruvate • Three-carbon product of glycolysis

  41. Aerobic Respiration Continues • Krebs cycle • Cyclic pathway that, along with acetyl CoA formation, breaks down pyruvate to CO2, netting 2 ATP and many reduced coenzymes

  42. Acetyl CoA Formation and the Krebs Cycle

  43. Mitochondrion outer membrane (next to cytoplasm) inner membrane inner mitochondrial compartment outer mitochondrial compartment (in between the two membranes) A An inner membrane divides a mitochondrion’s interior into an inner compartment and an outer compartment. The second and third stages of aerobic respiration take place at the inner mitochondrial membrane. Fig. 5-10a, p. 90

  44. Second Stage of Aerobic Respiration 2 pyruvate outer membrane (next to cytoplasm) inner membrane 6 CO 2 2 acetyl–CoA 2 ATP Breakdown of 2 pyruvate to 6 CO2 yields 2 ATP. Also, 10 coenzymes (8 NAD+, 2 FAD) combine with electrons and hydrogen ions, which they carry to the third and final stage of aerobic respiration. 8 NADH Krebs Cycle 2 FADH2 B The second stage starts after membrane proteins transport pyruvate from the cytoplasm to the inner compartment. Six carbon atoms enter these reactions (in two molecules of pyruvate), and six leave (in six CO2). Two ATP form and ten coenzymes accept electrons and hydrogen ions. Fig. 5-10b, p. 90

  45. The Krebs Cycle - details

  46. Electron Transfer Phosphorylation 4 2 5 3 1 Third Stage of Aerobic Respiration: Electron Transfer Phosphorylation Stepped Art Fig. 5-11, p. 91

  47. Summary: Aerobic Respiration C6H12O6 (glucose) + 6O2 (oxygen) + 36 ADP → 6CO2 (carbon dioxide) + 6H2O (water) + 36 ATP

  48. Aerobic Respiration glucose Cytoplasm A The first stage, glycolysis, occurs in the cell’s cytoplasm. Enzymes convert a glucose molecule to 2 pyruvate for a net yield of 2 ATP. 2 NAD + combine with electrons and hydrogen ions during the reactions, so 2 NADH also form. 4 ATP (2 net) ATP ATP Glycolysis 2 ATP 2 pyruvate 2 NADH Mitochondrion B The second stage occurs in mitochondria. The 2 pyruvate are converted to a molecule that enters the Krebs cycle. CO2 forms and leaves the cell. 2 ATP, 8 NADH, and 2 FADH2 form during the reactions. 6 CO2 Krebs Cycle ATP 2 ATP C The third and final stage, electron transfer phosphorylation, occurs inside mitochondria. 10 NADH and 2 FADH2 donate electrons and hydrogen ions to electron transfer chains. Electron flow through the chains sets up hydrogen ion gradients that drive ATP formation. Oxygen accepts electrons at the end of the chains. 8 NADH, 2 FADH2 ATP ATP ATP H2O Electron Transfer Phosphorylation oxygen 32 ATP Summary: Aerobic Respiration Stepped Art Fig. 5-9, p. 89

  49. Overview of aerobic respiration

  50. Where pathways start and finish

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