11-10-08_photosynthesis_CalvincycleA

11-10-08_photosynthesis_CalvincycleA - There is nothing in...

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There is nothing in the dark that isn't there when the lights are on. Rod Serling Outside of a dog, a book is a man's best friend. Inside of a dog it's too dark to read. Groucho Marx The light at the end of the tunnel is the front of an oncoming train. David Lee Roth, “Perfect Timing”
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Announcements Quiz 6 due at noon 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
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Reduction of NADP to NADPH requires ~ 2 V of redox potential Under standard conditions, oxidation of water and reduction of NADP are both unfavorable. Under conditions in the chloroplasts, the reactions are even more unfavorable Light is needed to drive the reaction
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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 charged P for pigment, number for wavelength absorbed PSII boosts electrons to a midway point PSI boosts electrons to above that of NADP+
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There can be only one: many chlorophyll molecules, one reaction center Incoming photons excite chlorophylls which very rapidly transmits energy to the reaction center The reaction center (P680 or P700) will accept the excited electron
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Light is absorbed to hydrolyze water and maintain a H+ gradient in photosystem II (PSII) 1) Light is absorbed by light harvesting complex II (LHC II) of photosystem II, which are chlorophylls and carotenoid pigment molecules bound to proteins. 2) Excited electrons propagate to the reaction center (P680), exciting it P680*. 3) P680* oxidizes to P680+ + e- and reduces pheophytin (Pheo-) 4) Pheo- transfers the electron in steps to plastoquinone B (PQ B ) to make PQ B - 5) Steps 1-4 are repeated to make (PQ B 2- ) Note: only one monomer of the LHCII dimer is shown
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Photolysis in photosynthesis After P680* donates an electron to make Pheo-, it becomes P680+ P680+ is a very powerful oxidizing agent , with a redox potential of +1.17 V, so it can overcome the -0.82 V barrier to hydrolyze water. 2 H
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This note was uploaded on 02/09/2010 for the course BIOL 230 taught by Professor Bartlett,e during the Fall '08 term at Purdue University-West Lafayette.

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11-10-08_photosynthesis_CalvincycleA - There is nothing in...

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