Lect_12_PSII

Lect_12_PSII - Photosynthesis II - CO 2 Fixation Carbon...

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Unformatted text preview: Photosynthesis II - CO 2 Fixation Carbon cycle Pathways of CO 2 fixation during PS History C-3 plant and the Calvin cycle carboxylation reduction regeneration Photorespiration C-4 plants and the Hatch-Slack pathway Reductive carboxylation in microorganisms Synthesis of starch Finish light reactions Second Midterm: Thursday, Nov. 15, 2007 Will primarily cover materials from lectures 7-12. Review session: Tuesday, Nov. 13, 2007 7:10 - 9:00 pm 1001 Giedt Hall A 1 P700 h γ h γ-1.4 cyt bf PC P700 P700 Fd Cyclic electron pathway ATP h γ BIS 103 - #11 - 3 - Photosynthesis - Hill-Bendall Scheme FP (Fd-NADP + oxido reductase) Fd (ferridoxin) FeS protein (phylloquinone) A o (electron accepting chl) NADP + NADPH + H + (non-cyclic) Q A Q B Ph (pheophytin) (plastoquinone) ADP + Pi ATP PC (plastocyanin) cyt bf complex Volts Photosystem II Photosystem I P700* P680*-0.432-0.32 Volts 0.0 +0.8 P680 (cyclic) ATP ADP + Pi-0.8 4e- + 4H + + O 2 2H 2 O Water splitting Mn complex ADP + Pi PS I How does the Z-scheme furnish the ATPs and NADPHs? 2 NADP + + 2H 2 O 2 NADPH + 2H + + O 2 2 ADP + 2Pi 2 ATP Cyclic photophosphorylation results in the following: ADP + Pi ATP 9 photons of light produced 3 ATPs and 2 NADPHs To reduce 1 CO 2 to CH 2 O, requires 3 ATPs and 2 NADPHs 4 photons activate PSI 4 photons activate PSII 1 photon activates PSI Non-cyclic photophosphorylation yields: BIS 103 - 11- PS - Quantum requirement for reducing CO 2 to C(H 2 O) CO 2 + 2 NADPH + 3 ATP + 2 H 2 O C(H 2 O) + 2 NADP + + 3 ADP + 3 Pi + O 2 + H 2 O Need one quantum to excite one electron How many quanta are required to reduce CO 2 to C(H 2 O)?- need 4 e- in PSI to synthesize 2 NADPH + H + = 4 quanta- need 4 e- in PSII to fill electron hole in PS1 & make 2ATPs = 4 quanta- need 1 e- in PSI to form 1 ATP by cyclic photophosphorl. = 1 quantum Therefore need 9 quanta of light to reduce 1 CO 2 to 1 C(H 2 O). Total = 9 quanta At 700 nm, 1 quantum (einstein ) of light contains about 176 kJ of energy Efficiency of photosynthesis : CO 2 + 2 H 2 O + n (hn) CH 2 O + H 2 O + O 2 ∆ G’ = + 477 kJ/mol 477/176 = 2.7 quanta or about 3 quanta of light are required to reduce CO 2 to C(H 2 O) at 100% efficiency. Green plants require 9 quanta, therefore efficiency is 3/9 x 100 = 33% efficiency Photosynthesis - CO 2 Fixation or dark reactions Carbon cycle Pathways of CO 2 fixation during PS History C-3 plant and the Calvin cycle carboxylation reduction regeneration Photorespiration C-4 plants and the Hatch-Slack pathway Reductive carboxylation in microorganisms Synthesis of starch Carbon cycle - page 51 The carbon cycle on earth involves photosynthesis by plants and microorganisms, which fix CO 2 into organic matter. CO 2 is produced by burning of fossil fuels and by catabolic metabolism of plants, animals, and microorganisms. Animals depend on the products of photosynthesis for their energy...
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This note was uploaded on 04/19/2008 for the course BIS 103 taught by Professor Abel during the Spring '08 term at UC Davis.

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Lect_12_PSII - Photosynthesis II - CO 2 Fixation Carbon...

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