Photosynthesis Life is Bottled Sunshine Wynwood Reade Martyrdom

Photosynthesis “Life is Bottled Sunshine” Wynwood Reade, Martyrdom of Man, 1872 Eva Farre, s 150

Topics 1. Overview of photosynthesis 2. Key early photosynthesis experiments 3. 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?

ATMOSPHERE COMPOSITION CONSTITUENT Nitrogen Oxygen Argon Carbon Dioxide Others CHEMICAL SYMBOL N 2 O 2 Ar CO 2 MOLE PERCENT 78. 084 20. 947 0. 934 0. 035 http: //www. globalchange. umich. edu/

H 20 + CO 2 CH 20 + O 2

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” (CO 2) 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

Photosynthesis is a redox reaction Where does the oxygen come from ? H 20 + CO 2 CH 20 + O 2 Van Niel (1920 s) analyzed the photosynthesis of purple bacteria: n. CO 2 + 2 n. H 2 O + light (CH 2 O)n + n. O 2 + n. H 2 O n. CO 2 + 2 n. H 2 S + light (CH 2 O)n + 2 n. S + n. H 2 O Hill equation (1937): H 20 + A + light ½ O 2 + H 2 A “Purple bacteria are the earliest emerging photosynthetic lineage” (Ziong et al. , 2000, Science) OXYGENIC / ANOXYGENIC photosynthesis LIGHT/ DARK or CARBON-LINKED reactions

(Des Marais, 2000. Science)

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

Oxygenic Photosynthesis ATP Light Reactions H 20 O 2 NADPH Carbon Reactions CO 2 CH 20

Chloroplast structure

Photosynthesis Light Reactions (Simplified) e-acceptor (NADP) e- ADP + Pi Reduced e-acceptor (NADPH) ATP Stroma ee-Donor (H 20) H+ Oxidized-e-Donor (O 2) H+ Thylakoid Lumen

Absorbance of light: Photochemistry

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

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

Photosynthetic Pigments Absorption Spectra

Photosynthetic Pigments : Structure

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

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)

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

Z- Scheme of photosynthesis

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

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