09-9 Photosynthesis with new slides

09-9 Photosynthesis with new slides - Photosynthesis The...

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Photosynthesis The harvesting of light energy ( photons ) and its storage as carbohydrates Organisms that photosynthesize are autotrophs (self-feeders): Purple sulfur bacteria (prokaryotes) USE SUNLIGHT TO CONVERT H2S  S Cyanobacteria, or bluegreen algae (prokaryotes) Green algae or phytoplankton Green plants CO2 is then reduced to carbohydrates in a separate set of reactions
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Photosynthesis Overview: Carbon dioxide + water + light energy  Glucose (C6H12O6) + oxygen Two distinct steps, light reactions and dark reactions: Light reactions – light energy cleaves water and creates ATP Dark reactions – carbon dioxide is assimilated into carbohydrates independent of light Freeman, Fig. 7.1 (Hill Reactions) (Calvin Cycle)
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Chloroplasts and Photosynthesis Leaf palisade and mesophyll cells are rich in chloroplasts Chloroplasts have complex, stacked membranes ( thylakoids ) Thylakoid membranes are filled with chlorophyll pigments
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Photosynthetic Pigments Hydrophobic tail, embedded in thylakoid membranes
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Photosynthetic Pigments Chlorophyll action spectra: Maximum absorbance of blue, red Minimal absorbance of green Therefore, plants reflect green light Freeman, Fig. 7.3
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Carotenoids Protect chlorophyll by absorbing free radicals Absorb light at wavelengths outside chlorophyll’s active spectrum and transfer energy to chlorophyll Components of the antenna complex Series of pigments that extend the effective range of chlorophyll a
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Photosystem II Feeding an Electron Transport Chain Chlorophyll e– In photosystem II, excited electrons feed an electron transport chain. Lower Photon E n e r g y o f l c t Pheophytin Cytochrome complex Higher PQ le a s p h in Plastoquinone carries protons to the inside of thylakoids, creating a proton-motive force. Photosystem II and the cytochrome complex are located in the thylakoid membranes 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 +
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Fate of 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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Light Reactions: the Z-Scheme Two photosystems: I and II Interconnected in the “Z-scheme” Localized in the thylakoid membranes Light energy cleaves water into protons, oxygen gas Electrons enter an electron transport chain Plastoquinone (PQ) transfers protons across the membrane into the grana Proton motive force phosphorylates ADP using ATP synthase photophosphorylation ferredoxin ferredoxin
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This note was uploaded on 04/05/2012 for the course HLTH 311 taught by Professor Anderson during the Spring '12 term at BYU.

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09-9 Photosynthesis with new slides - Photosynthesis The...

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