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Photosynthesis “Life is Bottled Sunshine” Wynwood Reade, Martyrdom of Man, 1872

Photosynthesis “Life is Bottled Sunshine” Wynwood Reade, Martyrdom of Man, 1872. Taiz & Zeiger: Chapters 7 & 8 Mo: Light reactions Wd: Light reactions/carbon reactions Fri: Carbon reactions. Eva Farre, s150. Topics Overview of photosynthesis Key early photosynthesis experiments

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Photosynthesis “Life is Bottled Sunshine” Wynwood Reade, Martyrdom of Man, 1872

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  1. Photosynthesis “Life is Bottled Sunshine” Wynwood Reade, Martyrdom of Man, 1872 Taiz & Zeiger: Chapters 7 & 8 Mo: Light reactions Wd: Light reactions/carbon reactions Fri: Carbon reactions Eva Farre, s150

  2. Topics • Overview of photosynthesis • Key early photosynthesis experiments • Photosynthesis: light reactions

  3. Clicker question: For the last 4 billion of years has been the oxygen concentration in the atmosphere constant? A. Yes, more of less. B. It fluctuated as did the Earth temperature. C. It started rising ~3 billion years ago. D. It has decreased. E. It started rising since the origin of earth.

  4. Oxygenic Photosynthesis Clicker question: A. CH2 B. ATP C. O2 D. NADPH E. H2O F. CO2 Light Reactions Carbon Reactions ? ? ? ? ? ?

  5. Oxygenic Photosynthesis Light Reactions Carbon Reactions ATP NADPH H20 O2 CO2 CH20

  6. Clicker question: What is the difference between the carbon in CO2 and the carbon in CH20? A. In CO2 the carbon is more oxidized than in CH2O. B. In CO2 the carbon is more reduced than in CH2O.

  7. Photosynthesis is a redox reaction Where does the oxygen come from ? H20 + CO2 CH20 + O2 Van Niel (1920s) analyzed the photosynthesis of purple bacteria: nCO2 + 2 nH2O + light  (CH2O)n + nO2 + nH2O nCO2 + 2nH2S + light  (CH2O)n + 2nS + nH2O Hill equation (1937): H20 + A + light  ½ O2 + H2A “Purple bacteria are the earliest emerging photosynthetic lineage” (Ziong et al., 2000, Science) OXYGENIC / ANOXYGENIC photosynthesis LIGHT/ DARK or CARBON-LINKED reactions

  8. William Martin*, John Baross‡, Deborah Kelley‡ and Michael J. Russell (Nat. Rev. Microbiology, 2008) The chemistry of life is the chemistry of reduced organic compounds, and therefore all theories for the origin of life must offer testable hypotheses to account for the source of these compounds. So, what happened before photosynthesis evolved?

  9. H20 + CO2 CH20 + O2

  10. Topics • Overview of photosynthesis • Key early photosynthesis experiments • Photosynthesis: light reactions

  11. History: From air to starch Stephen Hales (1677-1761): Plants assimilated “air” Joseph Priestley (1733–1804) : plants can “purify” air Jan Ingen-Housz (1730-1799): this was dependent on light Jean Senebier (1742–1809) :”fixed air” (CO2) is essential for photosynthesis Pierre Joseph Pelletier (1788– 1842) and Joseph Bienaimé Caventou (1795–1877): chlorophyll Hugo von Mohl (1805–1872) discovered chloroplasts in plant cells Julius Robert Mayer (1814–1878): plants convert light energy into chemical energy Julius von Sachs (1832–1897 ): starch granules are product of photosynthesis

  12. Topics • Overview of photosynthesis • Key early photosynthesis experiments • Photosynthesis: light reactions

  13. Oxygenic Photosynthesis Light Reactions Carbon Reactions ATP NADPH H20 O2 CO2 CH20

  14. Chloroplast structure

  15. Photosynthesis Light Reactions (Simplified) e-acceptor (NADP) ADP + Pi e- Reduced e-acceptor (NADPH) ATP Stroma Thylakoid Lumen e- H+ e-Donor (H20) H+ Oxidized-e-Donor (O2)

  16. Absorbance of light: Photochemistry

  17. Light absorption and emission of chlorophyll E = h (c/λ)

  18. Engelmann Experiments (1843 – 1909) Spyrogyra up to ~200 um long

  19. Photosynthetic Pigments Absorption Spectra

  20. Photosynthetic Pigments : Structure

  21. The Electron Transfer Process what happens to this "excited" electron? Energy

  22. The Electron Transfer Process Clicker question: What happens to this "excited" electron? 1. Excited chlorophyll re-emits a photon and returns to its ground state (fluorescence). 2. Excited chlorophyll returns to its ground state by directly converts its excitation energy to heat? 3. Excited chlorophyll transfers its energy to another pigment. 4. Energy is used to catalyze a chemical reaction. A: 1, 3 B: 1, 4 C: all C: 1, 2 D: 2, 3, 4

  23. Important photosynthesis concepts Photochemical quantum yield/ efficiency: Φ = Number of photochemical products Total number of quanta absorbed (energy of a photon) Energy efficiency: = Notal number of quanta absorbed Photosynthesis products (ATP/NADPH)

  24. The Electron Transfer Process Energy H20 2 H+ + ½ O2

  25. Red light enhancement effect (~1950s) : 2 photochemical complexes (~1960)

  26. Z- Scheme of photosynthesis

  27. Photosynthesis: Light Reactions

  28. Z-Scheme: Electron transfers (redox reactions)

  29. Photosynthesis: Light Reactions

  30. 7.31 Summary of the experiment carried out by Jagendorf and coworkers: the chemiosmotic mechanism

  31. Topics • Overview of photosynthesis • Key early photosynthesis experiments • Photosynthesis: light reactions

  32. What are the main open questions about the origin of oxygenic photosynthesis? Which are the current hypothesis to explain the beginning of oxygenic photosynthesis?

  33. Next lecture: -Genetics and Evolution of Photosynthetic Systems -Regulation of the Photosynthetic Machinery -Carbon reactions: Calvin-Benson cycle

  34. Monday’s Topics • Overview of photosynthesis • Key early photosynthesis experiments • Photosynthesis: light reactions

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