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Photosynthesis

Photosynthesis. Photosynthesis with Hank!. Life from Light and Air. Obtaining the materials. sunlight leaves = solar collectors CO 2 stomates = gas exchange H 2 O uptake from roots nutrients N, P, K, S, Mg, Fe… uptake from roots. Concurrent Reactions.

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Photosynthesis

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  1. Photosynthesis Photosynthesis with Hank! LifefromLight andAir

  2. Obtaining the materials • sunlight • leaves= solar collectors • CO2 • stomates = gas exchange • H2O • uptake from roots • nutrients • N, P, K, S, Mg, Fe… • uptake from roots

  3. Concurrent Reactions

  4. *Key to these rxns is light absorption Success lies in photosystems – 2 part complex Light-Dependent Reactions Antenna complex – site of absorption; excites electrons & passes them on Reaction center – redox-rxns occur here; excited ele- transferred to electron acceptor

  5. reactioncenter antennapigments

  6. To Calvin Cycle!!! Stroma ATP! NADPH ADP + P NADP + + 2H + PS 700 PS 680 H+ + ½ O2 + Lumen - NADP+Reductase - Cytochromecomplex - ferredoxin - pheophytin - ATP Synthase - ele - - plastoquinone - H + ion

  7. Step 1: Light absorbed in PS II excites ele- (from H2O splitting) → passed to electron acceptor (pheophytin) Step 2: Plastoquinone(PQ) shuttles high energy ele- through series of redoxrxns (ETC 1); passes through cytochrome complex, driving in H+, ↑ [H+] = ↓ pH Step 3: De-energized ele- are passed off to plastocyanin (PC) → PS I re-excites ele- and ferredoxinshuttles through ETC 2 Step 4: a) Ele- reduce NADP+ to NADPH at NADP+ reductase b) H+ pumped out via ATP Synthase – activateschemiosmosis→production of ATP from ADP

  8. Regulation of the Light Reaction • Calvin cycle uses more ATP than NADPH • If there is enough, NADPH production is turned off ATP 18 ATP +12 NADPH  1C6H12O6

  9. Review Animations • Light dependent reactions

  10. Light-INdependent Reactions C6H12O6 NADP • Want to make C6H12O6 → synthesis **How? From what? What raw materials are available? CO2 NADPH reduces CO2 carbon fixation NADP

  11. From CO2 C6H12O6 • CO2 has very little chemical energy • fully oxidized • C6H12O6has a LOTof chemical energy • highly reduced • Synthesis = endergonic process • put in a lot of energy • Reduction of CO2C6H12O6proceeds in many small uphill steps • each catalyzed by specific enzyme • uses energy stored in ATP & NADPH ←from light rxns!

  12. 5C 1C 3C 3C CO2 C 5C C 3 ATP C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C 3 ADP 3C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C 6C = = C C C 6 ATP 6 NADPH H H H H H H | | | | | | – – C C C 6 NADP 6 ADP Calvin cycle C C C 1. Carbon fixation 3. Regenerationof RuBP RuBP RuBisCo ribulosebisphosphate starch,sucrose,cellulose& more ribulosebisphosphatecarboxylase used to makeglucose glyceraldehyde-3-P PGA G3P aka PGAL phosphoglycerate 2. Reduction

  13. To G3Pand beyond! To G3P and Beyond! • Resulting 3-C Sugar - important intermediate • G3P glucose  carbohydrates  lipids phospholipids,fats, waxes  amino acids proteins  nucleic acids DNA, RNA

  14. Enzyme which fixes carbon from air • ribulosebisphosphatecarboxylase • the most important enzyme in the world! **It makes life out of air!** • most abundant enzyme A little more about RuBisCo…

  15. “Banking” • Keeping the books straight… • 6 turnsof Calvin cycle = 1C6H12O6(6C) • 6 CO2 1C6H12O6(6C) • 18 ATP+ 12 NADPH 1C6H12O6 • Left over ATPfrom light reactions used elsewhere by cell

  16. light energy  H2O + + + O2 ATP NADPH sunlight Sum it Up: Light Reactions H2O • produces ATP & NADPH • releases O2as waste Energy Building Reactions NADPH ATP O2

  17. CO2 + + + + ATP NADPH C6H12O6 ADP NADP Calvin Cycle • builds sugars • uses ATP & NADPH • recycles ADP & NADP+ CO2 ADP NADP SugarBuilding Reactions NADPH ATP sugars

  18. Supporting a biosphere • Big Picture: photosynthesis is THE most important process for continuation of life on Earth • Each year photosynthesis… • captures 121 billion tons of CO2 • synthesizes 160 billion tons of carbohydrates • heterotrophs depend on plants for food, fuel, & raw materials

  19. Where did the energy come from? • Where did the electrons come from? • Where did the H2O come from? • Where did the O2 come from? • Where did the O2 go? • Where did the H+ come from? • Where did the ATP come from? • What will the ATP be used for? • Where did the NADPH come from? • What will the NADPH be used for? Light Depedent Review:

  20. light energy  6CO2 6H2O 6O2 + + C6H12O6 + Light Independent Review II: • Where did the CO2 come from? • Where did the CO2 go? • Where did the H2O come from? • Where did the H2O go? • Where did the energy come from? • What’s the energy used for? • What will the C6H12O6 be used for? • Where did the O2 come from? • Where will the O2 go? • What else is involved…not listed in this equation?

  21. C4 Path • CO2 stored is mesophyll & released in vascular tissue Adaptations in Alternative Environments

  22. CAM Path • Stomata open at night – CO2 stored in vacuoles for later use Adaptations in Alternative Environments

  23. Photorespiration – rxn between RuBP & O2 when [O2] is high → uses ATP & produces CO2 Combating Photorespiration Favored ONLY when [O2] exceeds [CO2] Store CO2 C4 Path CAM Plants

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