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Photosynthesis“Life is Bottled Sunshine”
Wynwood Reade, Martyrdom of Man, 1872
Eva Farre, s150
Topics
1.Overview of photosynthesis2.Key early photosynthesis experiments3. Photosynthesis: light reactions
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?
CONSTITUENT CHEMICAL SYMBOL MOLE PERCENTNitrogen N2 78.084Oxygen O2 20.947Argon Ar 0.934Carbon Dioxide CO2 0.035Others
ATMOSPHERE COMPOSITION
http://www.globalchange.umich.edu/
H20 + CO2
CH20 + O2
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
Where does the oxygen come from ?
Photosynthesis is a redox reaction
H20 + CO2CH20 + O2
Van Niel (1920s) analyzed the photosynthesis of purple bacteria:
nCO2 + 2 nH2O + light (CH2O)n + nO2 + nH2OnCO2 + 2nH2S + light (CH2O)n + 2nS + nH2O
(Ziong et al., 2000, Science)
“Purple bacteria are the earliest emerging photosynthetic lineage”
OXYGENIC / ANOXYGENIC photosynthesis LIGHT/ DARK or CARBON-LINKED reactions
Hill equation (1937): H20 + A + light ½ O2 + H2A
(Des Marais, 2000. Science)
Topics
1.Overview of photosynthesis2.Key early photosynthesis experiments3. Photosynthesis: light reactions
Oxygenic Photosynthesis
Light ReactionsLight ReactionsATP
NADPHCarbon
ReactionsCarbon
Reactions
H20 O2 CO2 CH20
Chloroplast structure
Photosynthesis Light Reactions(Simplified)
e-e-
e-e-
e-Donor (H20)Oxidized-e-Donor (O2)
e-acceptor (NADP)
Reduced e-acceptor (NADPH)
H+
H+
ADP + Pi
ATP
ThylakoidLumen
Stroma
Absorbance of light: Photochemistry
E = h (c/λ)
Light absorption and emission of chlorophyll
Engelmann Experiments(1843 – 1909)
Spyrogyra up to ~200 um long
Photosynthetic Pigments Absorption Spectra
Photosynthetic Pigments : Structure
ChlorophyllOrganism a b c d Carotinoids Phycobilins
Plants + + - - + -Green algae + + - - + -Diatoms + - + - + -Dinoflagelates + - + - + -Brown and yellow algae + - + - + -Red algae + - - + + -Cyanobacteria + - - - + +
Photochemical quantum yield/ efficiency:
Φ = Number of photochemical productsTotal number of quanta absorbed (energy of a photon)
Energy efficiency:
= Notal number of quanta absorbedPhotosynthesis products (ATP/NADPH)
Important photosynthesis concepts
Red light enhancement effect (~1950s) : 2 photochemical complexes (~1960)
Z- Scheme of photosynthesis
Topics
1.Overview of photosynthesis2.Key early photosynthesis experiments3. Photosynthesis: light reactions
Next lecture:-Electron Transport Details (check respiration)-Regulation of the Photosynthetic Machinery-Genetics and Evolution of Photosynthetic Systems