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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. Eva Farre, s150. Topics Overview of photosynthesis Key early photosynthesis experiments Photosynthesis: light reactions. Where does the oxygen in the atmosphere come from?

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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 Eva Farre, s150

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

  3. Where does the oxygen in the atmosphere come from? Was the oxygen concentration constant? What are the necessary components of photosynthesis? What is the overall reaction of photosynthesis? Which is the order of events?

  4. ATMOSPHERE COMPOSITION CONSTITUENT CHEMICAL SYMBOL MOLE PERCENT Nitrogen N2 78.084 Oxygen O2 20.947 Argon Ar 0.934 Carbon Dioxide CO2 0.035 Others http://www.globalchange.umich.edu/

  5. H20 + CO2 CH20 + O2

  6. 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

  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. (Des Marais, 2000. Science)

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

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

  11. Chloroplast structure

  12. 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)

  13. Absorbance of light: Photochemistry

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

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

  16. Photosynthetic Pigments Absorption Spectra

  17. Photosynthetic Pigments : Structure

  18. Chlorophyll Organism a b c d Carotinoids Phycobilins Plants + + - - + - Green algae + + - - + - Diatoms + - + - + - Dinoflagelates + - + - + - Brown and yellow algae + - + - + - Red algae + - - + + - Cyanobacteria + - - - + +

  19. 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)

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

  21. Z- Scheme of photosynthesis

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

  23. Next lecture: -Electron Transport Details (check respiration) -Regulation of the Photosynthetic Machinery -Genetics and Evolution of Photosynthetic Systems

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