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10 calvin cycle-plant limitations-2010 stacy

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    10 calvin cycle-plant limitations-2010  stacy 10 calvin cycle-plant limitations-2010 stacy Presentation Transcript

    •  
    • Calvin Cycle
    • Calvin Cycle Overview
      • Calvin cycle is a cyclical process which:
      • Fixes carbon (make C-C bonds)
      • Utilizes energy molecules
      • Regenerates molecules for another cycle
    • Calvin Cycle
      • occurs in the stroma of chloroplast
      • reactions are not as linear as Krebs
    • 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
    • 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
    • Calvin Cycle: Energy Utilization
      • ATP phosphorylates each 3-carbon molecule
      • rxn type: phosphorylation
      • enzyme: kinase
      • energy: absorbed
    • Calvin Cycle: Energy Utilization
      • NADPH used to synthesize G3P
      • rxn type: redox
      • enzyme: dehydrogenase
      • energy: absorbed
    • 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
    • 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
    •  
    • Factors Overview
      • light intensity, [CO 2 ] and temperature
      • C3 plant limitations
      • C4 plants
      • CAM plants
    • Photosynthesis Rate Photosynthesis Rate
    • 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
    • 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?
    •  
    • 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
    • C4 Plant Adaptation
      • adaptation to hot, arid environments
      e.g. corn, sugarcane, grasses
    • 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.
    • 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.
    • 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