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Announcements, March 12

Announcements, March 12

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Announcements, March 12

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  1. Announcements, March 12 • Please remove homework from folders • One homework and 2 quizzes (Q14, Q18) without names still unclaimed – please see me to claim. • Reading for today: pp. 288-302 on photosynthesis; pp. 302-307 will not be covered due to snow day. • Review Session from 4-5 PM, March 13 in BR 203 • Exam 2 on Wednesday, March 14 over the same material as before. • Reading for Friday, March 16: pp. 318-358 on intracellular trafficking

  2. Chloroplast Ultrastructure

  3. Photosynthesis Overview • Light + 3 CO2 + 6 H2O → C3H6O3 + 3 O2 + 3 H2O • Function: ATP synthesis and synthetic rxns • Energy source: sunlight • Energy conversion: • solar  H+ gradient  ATP • H2O  electron transport  NADPH • Carbon source: CO2 • Electron source: H2O • Intermediate electron acceptor: NADP+ • Byproduct: O2 Reduced C: 3C sugar

  4. Energy Transduction reactions: Photoreduction (NADPH synthesis) Photophosphorylation (ATP synthesis)

  5. NADP+ and NADPH Carry e- in synthetic reactions, whereas NAD+/NADP used in degradative rxns.

  6. Absorption spectra of plant pigments

  7. Chlorophyll Chlorophyll is special because it can accept a low energy electron and donate a high energy electron.

  8. Light Harvesting Complex 1. Heat, light 2. 3.

  9. Fate of light energy when e*  eo • Energy is lost as heat and lower energy light. • Resonance energy transfer to an electron in an adjacent pigment molecule. • Photochemical reduction, where e* is itself transferred to a carrier (only in reaction center chlorophyll).

  10. Resonance Energy Transfer to Adjacent Pigments Excited state e* eo e* eo e* eo e* eo photon Ground state Reaction center chlorophyll P680 PSII Antenna chlorophylls

  11. Photochemical Reduction:e* is transferred to NADP+ e* eo NADP+  NADPH photon OEC ETS e* eo e* e* e e* H2O  2H+ + O2 Reaction center chlorophyll P680 PSII Electron transport System (ETS) Chlorophyll P700 PSI

  12. Energy conversion in thylakoid MB Analogous To RCIII

  13. The Z Scheme: Steps 1. Water splitting: 2 H2O → 4 H+, O2 to lumen 2. P680o P680* (PSII) 3. Electron transfer to P700o (PSI) 4. 4 H+ pumped to lumen through cytochrome b6/f 5. P700o  P700* (PSI) 6. Electron transfer to ferredoxin 7. Ferredoxin-NADP+ reductase catalyzes: 2 NADP+ + 2 H+stroma + 2 e-  2 NADPH

  14. Understanding how the water-splitting enzyme works is a major unsolved problem, with practical applications 4

  15. Z scheme

  16. H+ Cl- lumen stroma lumen stroma H+ H+ Mg2+ Photophosphorylation(Light-driven ATP synthesis) Current estimates (know this): • pHlumen = 6 • pHstroma = 8 • pH = -2 (in-out) • Em = +30 mV (flow of Mg2+ and Cl- balances much of flow of H+) • pmf = 30 - 60 mV(-2) = +150 mV • 4 H+ flow/ATP through CF0CF1 ATP synthase • 4 e- Z scheme  2 ATP, 2 NADPH • But need 3 ATP/2 NADPH in Calvin cycle, so cyclic electron flow occurs:

  17. Cyclic e- Flow • Regulates NADPH/ATP formed (need 2:3). • 2 electrons flow back through cyt b6/f to P700, pumping 4 H+ into lumen • 2 photons re-excite the 2 electrons. • No water oxidized and no O2 released, since PSII not involved. NADP+ PSI

  18. Photosynthesis Reactions(Don’t memorize) 1. Energy transduction reactions (Equation 11-14) 26 photons + 9 ADP + 9 Pi + 6 NADP+ + 6 H2O  3 O2 + 9 ATP + 6 NADPH + 3 H2O 2. Calvin cycle reactions (Equation 11-13) 3 CO2 + 9 ATP + 6 NADPH + 6 H2O  C3H6O6 + 6 NADP+ + 9 ADP + 9 Pi 3. Overall (Equation 11-16): 26 photons + 3 CO2 + 6 H2O  C3H6O6 + 3 O2 + 3 H2O What % of mass of C3H6O6 comes from CO2 ? MW of CO2 is 44, of H2O is 18, of C3H6O6is 186.

  19. Carbon fixation occurs in the stroma