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Lect_12_notes - in mitochondria and NADPH for use in Calvin...

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Lecture 12 Notes Bio 1A Professor Schlissel February 20, 2008 Photosynthesis: The Light and Dark Reactions 1. A comparison of the overall reactions of respiration and photosynthesis. Where does the energy come from? 2. Structure of the chloroplast and the thylakoid membranes. 3. Light reactions generate ATP and NADPH which are used to “fix” carbon in the form of CO 2 into sugars via the Calvin cycle. 4. The absorption of light by pigments. Chlorophyll, b-carotene. Absorption spectra. Resonance energy transfer (RET). 5. The photosystem—a set of antenna molecules to capture photons and to transfer energy from them to the reaction center. Two special chlorophylls in reaction center, bound to proteins, which transfer excited electron to primary electron acceptor. Also, serves as oxidizing agent to split water into O 2 and H + . 6. Photosystem I and Photosystem II. P700 and P680. Linked in non-cyclic electron flow (also called “Z-scheme”) to generate proton motive force (resulting in ATP synthesis as
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Unformatted text preview: in mitochondria) and NADPH for use in Calvin cycle. 7. Cyclic electron flow—photosystem I uses light energy to make ATP, but NOT NADPH. Unlinked from PS II. 8. Orientation of ATP synthase in chloroplasts as compared to mitochondria. 9. Carbon fixation by the Dark Reactions. Ribulose biphosphate carboxylase (“Rubisco”) is the key enzyme which adds CO 2 to RuBP and generates 2 molecules of 3-phosphoglycerate. Calvin cycle then uses ATP and NADPH to convert these into glyceraldehyde 3-phosphate which can be used to synthesize glucose. 10. Its more complicated than this. CO 2 is sometimes limiting so plants have to find additional ways to hold on to CO 2 while not losing too much water. 11. Photorespiration occurs when O 2 concentration is high. RuBisCO uses O 2 instead of CO 2 to generate 3-phosphoglycerate and glycolate. Glycolate metabolism releases CO 2 back to the environment in a reaction which uses ATP, reversing the effects of photosynthesis. Why would such a pathway exist?...
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