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