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Unformatted text preview: 1 some concepts of photosynthesis General Overview- Light and Dark Reactions Light Reactions Occur in chloroplasts Goal-- to make ATP for synthesis of sugars Photosystems and light harvesting Electron Flow Electron Transport Complexes Absorption of photons- photosystems I and II Proton gradient (Proton motive force) Chlorophyll, plastoquinone, cytochrome bf, Fd-NADP + reductase Readings in Textbook : pages 541-557 Practice Problems : Pages 563-564- #1, 3, 4, 8 The Light and Dark Reactions of Photosynthesis If you’re brave- Photosynthesis A Musical Lecture Part A and Part B Explore Photosynthesis 1 Explore Photosynthesis 2 Chloroplasts (& mitochondria) arose from an endosymbiotic event Meyerowitz 2002. 2 Thylakoid membrane Thylakoid space Stroma The Light Reactions of Photosynthesis Site is the thylakoid membrane Four electron transport complexes Two of these ( photosystem I and II ) that harvest light energy Terminal acceptor of electrons is NADPH O 2 is “evolved” not “consumed” Proton motive force is generated by H + transport inside thylakoid ATP synthase harvests this and produces ATP inside stroma CO 2 + H 2 O CH 2 O + O 2 Why is light energy needed for the light reactions of photosynthesis? 2 H 2 O + 2 NADP + → O 2 + 2 NADPH + 2H + ΔG o’ = +440 kJ/mol Electrons are moving from +E o’ to –E o’ This is energetically unfavorable and energy in the form of light is needed The “Z-scheme” Folow link to see: Footbal description of Z scheme from Ohio State Footbal team Light is harvested by chlorophyll pigments in Photosystem I and II Chlorophyll a : cyclic tetrapyrrole similar to heme...
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