Lecture 11 - 6:1 - Biology 172 Lecture 11 Wednesday June 1...

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Lecture 11: Wednesday June 1, 2011 Biology 172 Today’s Outline Announcements Exam: Friday in  class Office hours :  Thursday night 7 to  8.30pm Photosynthesis Light Reactions Noncyclic Electron Flow Cyclic Electron Flow Calvin Cycle
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Figure 10-11 Three Fates for Excited Electrons in Photosynthetic Pigments Reaction center Fluorescence Heat Photon Photon e e Electron acceptor Chlorophyll molecules in antenna complex Reaction center Chlorophyll molecule Lower Higher E n e r g y o f l c t RESONANCE FLUORESCENCE REDUCTION/ OXIDATION or or e Electron drops back down to lower energy level; heat and fluorescence are emitted. Electron is transferred to a new compound. Energy in electron is transferred to nearby pigment.
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Figure 10-15 Noncyclic electron flow (Z-Scheme) during the light reactions links PSII and PSI , and generates ATP and NADPH 4e 4 Photons E n e r g y o f l c t 2 H + 2 NADP + 2 NADPH Lower Higher Photosystem I Ferredoxin T C + 4e 4 Photons 4e Photosystem II 4 H + PQ PC P700 ATP produced via proton-motive force Cytochrome complex Pheophytin P680 + O 2 2 H 2 O What happens to the high energy electrons transferred from Reaction Center?
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Figure 10-13 Photon e Chlorophyll 1. Photons of light excite electrons from photosystem (PS II) chlorophylls P680 How does Photosystem II (PSII) work?
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Higher Energy of electron Lower Photon e e Chlorophyll Pheophytin Figure 10-13 2. Excited chlorophyll electrons are passed to primary electron acceptor (Pheophytin) 1. Photons of light excite electrons from photosystem (PSII ) chlorophylls P680
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Higher Energy of electron Lower Photon e e e Chlorophyll Pheophytin Cytochrome complex PQ E l e c t r o n a s p h i Figure 10-13 3. Electrons accepted by Pheophytin are transferred to PQ, and then passed down the electron transport chain to the cytochrome complex P680
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Figure 10.13 How a photosystem harvests light Cytochrome complex PQ PQ e e e Pheophytin Antenna complex Reaction center Photosystem II Stroma Photon H + H + Thylakoid lumen (low pH) H + H + H + H + H + H + H + H + H + H + H + 5. The electrons are passed to the cytochrome complex 4. PQ carries electrons from PSII, along with protons from the stroma 6. The protons are released into the thylakoid lumen
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Lower Energy of electron 4 Photons Pheophytin 4e 4e P680 2 H 2 O 4 H + + O 2 Photosystem II PQ Cytochrome complex PC ATP produced via proton-motive force E l e c t r o n a s p Figure 10-15 Protons are pumped across thylakoid membrane into thylakoid lumen and used to make ATP Electrons are passed down electron transport chain to PC (plastocyanin)
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Lecture 11 - 6:1 - Biology 172 Lecture 11 Wednesday June 1...

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