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

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Presentation on theme: "Photosynthesis “Life is Bottled Sunshine” Wynwood Reade, Martyrdom of Man, 1872 Eva Farre, s150 Taiz & Zeiger: Chapters 7 & 8 Mo: Light reactions Wd: Light."— Presentation transcript:

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

2 Topics 1.Overview of photosynthesis 2.Key early photosynthesis experiments 3. 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 Light Reactions ???? Carbon Reactions ? ? Clicker question: A. CH2 B. ATP C. O2 D. NADPH E. H2O F. CO2

5 Oxygenic Photosynthesis Light Reactions ATP NADPH Carbon Reactions H 2 0 O 2 CO 2 CH 2 0

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 Where does the oxygen come from ? Photosynthesis is a redox reaction 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 (Ziong et al., 2000, Science) “Purple bacteria are the earliest emerging photosynthetic lineage” OXYGENIC / ANOXYGENIC photosynthesisLIGHT/ DARK or CARBON-LINKED reactions Hill equation (1937):H20 + A + light  ½ O2 + H2A

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 1.Overview of photosynthesis 2.Key early photosynthesis experiments 3. Photosynthesis: light reactions

11 History: From air to starch Stephen Hales ( ): Plants assimilated “air” Joseph Priestley (1733–1804) : plants can “purify” air Jan Ingen-Housz ( ): 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 1.Overview of photosynthesis 2.Key early photosynthesis experiments 3. Photosynthesis: light reactions

13 Oxygenic Photosynthesis Light Reactions ATP NADPH Carbon Reactions H 2 0 O 2 CO 2 CH 2 0

14 Chloroplast structure

15 Photosynthesis Light Reactions (Simplified) e- e-Donor (H 2 0) Oxidized-e-Donor (O 2 ) e-acceptor (NADP) Reduced e-acceptor (NADPH) H+H+ H+H+ ADP + Pi ATP Thylakoid Lumen Stroma

16 Absorbance of light: Photochemistry

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

18

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

20 Photosynthetic Pigments Absorption Spectra

21 Photosynthetic Pigments : Structure

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

23 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

24 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) Important photosynthesis concepts

25 Energy H20H20 2 H + + ½ O 2 The Electron Transfer Process

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

27 Z- Scheme of photosynthesis

28 Photosynthesis: Light Reactions

29 Z-Scheme: Electron transfers (redox reactions)

30 Photosynthesis: Light Reactions

31 7.31 Summary of the experiment carried out by Jagendorf and coworkers: the chemiosmotic mechanism

32 Topics 1.Overview of photosynthesis 2.Key early photosynthesis experiments 3. Photosynthesis: light reactions

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

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

35 Monday’s Topics 1.Overview of photosynthesis 2.Key early photosynthesis experiments 3. Photosynthesis: light reactions


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