10 calvin cycle-plant limitations-2010 stacy

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Transcript

  • 1.  
  • 2. Calvin Cycle
  • 3. Calvin Cycle Overview
    • Calvin cycle is a cyclical process which:
    • Fixes carbon (make C-C bonds)
    • Utilizes energy molecules
    • Regenerates molecules for another cycle
  • 4. Calvin Cycle
    • occurs in the stroma of chloroplast
    • reactions are not as linear as Krebs
  • 5. Calvin Cycle: Carbon Fixation
    • three CO 2 (1 carbon) are attached to three 1,5-ribulose bisphosphate (5 carbon)
    • three 6-carbon molecule are split into six 3-carbon molecules
    rxn type: synthesis enzyme: synthase ( Rubisco ) energy: absorbed
  • 6. Rubisco
    • r ib u lose bis phosphate c arboxylase / o xygenase
    • large, slow reacting enzyme
      • most enzymes process 1000 reactions / second
      • rubisco processes 3 reactions / second
    • plants need large amounts of rubisco for Calvin cycle
      • half the protein in a leaf
      • most abundant protein on Earth
  • 7. Calvin Cycle: Energy Utilization
    • ATP phosphorylates each 3-carbon molecule
    • rxn type: phosphorylation
    • enzyme: kinase
    • energy: absorbed
  • 8. Calvin Cycle: Energy Utilization
    • NADPH used to synthesize G3P
    • rxn type: redox
    • enzyme: dehydrogenase
    • energy: absorbed
  • 9. Calvin Cycle: Regenerate Molecules
    • 5 G3P and ATP to resynthesize 1,5-ribulose bisphosphate
    • 1 G3P used in another pathway
    • rxn type: synthesis
    • enzyme: synthase
    • energy: absorbed
  • 10. Calvin Cycle Review
    • 6 turns of the Calvin cycle to fix 6 CO 2 molecules
    • 18 ATP & 12 NADPH molecules used
    • electrons from 10 H 2 O transferred through the light reactions
  • 11.  
  • 12. Factors Overview
    • light intensity, [CO 2 ] and temperature
    • C3 plant limitations
    • C4 plants
    • CAM plants
  • 13. Photosynthesis Rate Photosynthesis Rate
  • 14. Photosynthesis Rate Factors
    • increased [CO 2 ] = increased photosynthesis
    • increased temperature = increased photosynthesis
    • increased light intensity = increased photosynthesis
      • only to a certain plateau since Calvin cycle cannot keep up with the light reactions
  • 15. C3 Plant Limitations
    • C3 plants undergo photosynthesis as described
    • stomata are open during the day / closed at night
    • What happens to stomata in hot, arid conditions?
  • 16.  
  • 17. C3 Plant Limitations
    • In hot, arid conditions, plants close the stomata and increases [O 2 ] within the cells.
    • At high [O 2 ], rubisco binds to O 2 rather than CO 2 in the process of photorespiration that causes the plant to skip the Calvin cycle. Glucose is not produced.
    • This is detrimental to agricultural crops.
      • rice, wheat, soy
  • 18. C4 Plant Adaptation
    • adaptation to hot, arid environments
    e.g. corn, sugarcane, grasses
  • 19. C4 Plant Adaptation
    • C4 plants have a special mesophyll cell & bundle-sheath cell structure.
    • Mesophyll cells create 4-carbon molecules using PEP carboxylase and release CO 2 into the bundle-sheath cells.
    • Bundle-sheath cells only perform the Calvin cycle.
    • In hot, arid conditions, C4 cells provide enough CO 2 to ensure rubisco does not bind to O 2 molecules.
  • 20. CAM(crassulacean acid metabolism) Plant Adaptation
    • adaptation to hot, arid environments
    • e.g. cactus, pineapples (water storing plants)
    • Stomata are closed in the day and open at night.
  • 21. CAM Plant Adaptation
    • CO 2 collected & incorporated into organic molecules at night
    • CO 2 released from the organic molecules during the day where ATP & NADPH is produced to allow the Calvin cycle to proceed