10-14-11_photosynthesis_CalvincycleB

10-14-11_photosynthesis_CalvincycleB - Uproot your...

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Uproot your questions from their ground and the dangling roots will be seen. More questions! – Mentat Zensufi (Dune ) The Brain : Are you pondering what I'm pondering? Pinky : Woof, oh, I'd have to say the odds of that are terribly slim, Brain. The Brain : True. Pinky : I mean, really, when have I ever been pondering what you've been pondering? The Brain : To my knowledge, never. Pinky : Exactly. So, what are the chances that this time, I'm pondering what you're pondering? The Brain : Next to nil. Pinky : Well, that's exactly what I'm thinking, too. The Brain : Therefore, you ARE pondering what I'm pondering. Pinky : Poit, I guess I am.
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Announcements The next quiz will be posted this Friday or Saturday and will cover the electron transport chain and ATP synthesis by ATP synthase. It will be due the following Wednesday (10/19). I will discuss the CELLLS project on Monday. Nothing is due on Monday.
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Summary of the two major electron transport processes in plant cells
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Chloroplasts Outer envelope membrane Inner envelope membrane Thylakoids – flattened membranous sacs in stacks called *grana* Chlorophyll in thylakoids Space outside – stroma; inside – lumen Stroma contains DNA High [H+] in lumen, low in stroma
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Changing to use of H 2 0 poses a serious redox problem 2 H 2 S → 2 S, E°’ = +0.25 V 2 H 2 0 → O 2 , E°’ = - 0.82 V (Note that the Karp book lists the E°’ for the reverse reduction reaction) To use water, a strong oxidizing agent is needed to overcome the redox potential and oxidize water. “Whereas respiration in mitochondria reduces oxygen to water, photosynthesis oxidizes water to oxygen” - Karp
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Photolysis Energy from the sun … Splits water 2 H 2 O 4 H + + O 2 + 4 e - (requires 4 photons) Very difficult Oxygen is the byproduct In the lab, splitting of water requires a lot of energy Electricity Temperatures around 2000 o C “splitting of water is the most thermodynamically challenging (endergonic) reaction known to occur in living organisms… Yet a plant cell can accomplish this feat on a snowy mountainside using only the energy of visible light” (Karp 216).
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Light-Reaction (Z-scheme): Transfer of light energy to chemical energy Whole point is to form ATP and NADPH Energy is absorbed by PSII Light strikes, energy absorbed by antenna pigments Electrons passed to reaction centers Electrons travel to primary electron receptor; reaction centers become positively
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10-14-11_photosynthesis_CalvincycleB - Uproot your...

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