光合作用机制英文讲义.ppt

Photosynthesis -- the legend of Prometheus Outline Biochemistry of Photosynthesis The light reaction: harvesting light energy The dark reaction: CO2 fixation C4 Photosynthesis Photorespiration C4 plants – a solution of low CO2 environment CAM Photosynthesis– adaptation to drought Can C4 and CAM photosynthesis pathways exist in the same plant? Photon Absorption by Pigments Four stages of the light reactions Primary Photoevent – light absorption by a pigment and an electron is excited Charge Separation – reaction center transfers an electron to an acceptor molecule Electron transport – excited electron shuttled from one compound to the next resulting in the formation of a proton gradient Chemiosmosis – the proton gradient is used to form ATP Hundreds of pigment molecules are clustered in antenna complexes Light Reactions of Photosynthesis Light energy is Absorbed Electrons transported (Redox Reaction) From H2O To NADPH ATP is formed Oxygen is produced Light independent or “Dark” Reactions Requires the products of the Light Reactions Stroma (in Chloroplast) Carbon dioxide fixation Sugar formation Enzyme mediated Multiple variations Photosynthesis captures energy from sunlight for the biosphere – Prometheus, who brought the human beings fire the conversion of light-energy to chemical-energy in the chloroplasts of eukaryotic cells high efficiency (20-30% of absorbed light), using 2-3% of irradiation generates 120 billion metric tons of sugar annually - ultimately nearly all of the carbon in the biosphere! is the process by which energy enters the biosphere Has produced all of the Oxygen in the Atmosphere C4 Photosynthesis The first product of carbon fixation has 4 carbon atoms C4 photosynthesis add one CO2 concentrating system on the base of C3 photosynthesis Adaptation to low atmosphere CO2 concentration in earth history RubiscoRibulose-1,5-bisphosphate carboxylase/oxygenase Catalyzes CO2 + RuBP 2 PGA Also catalyzes 02 + RuBP PGA + PG