Photosynthesis Calvin Cycle


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  • - compare and contrast mitochondria and chloroplast structure
  • Photosynthesis Calvin Cycle

    1. 1. Calvin CycleAdaptationsFactors Affecting RatePhotosynthesis Part 2
    2. 2. Calvin Cycle
    3. 3. Calvin cycle occurs in the stromaIntermembrane Space/Thylakoidspace
    4. 4. Calvin Cycle OverviewCyclical process with 3 phases:Carbon fixation: incorporation of CO2Reduction: utilization of energy molecules toform organic compoundRenegeration: regenerates molecules foranother cycle
    5. 5. Calvin Cycle Overview
    6. 6. Phase 1: Carbon FixationCO2 (1c) + 1,5-RuBP (5c) = shortlived 6Cintermediate6C molecule splitinto two 3Cmolecule known as3-PGA/PGA/3PGAbove reactionoccurs 3x reaction type: synthesis enzyme: synthase (Rubisco) energy: absorbed(3-PGA or PGA or 3PG)
    7. 7. Rubiscoribulose bisphosphate carboxylase /oxygenaselarge, slow reacting enzymemost enzymes process 1000 reactions / secondrubisco processes 3 reactions / secondplants need large amounts of rubisco forCalvin cyclehalf the protein in a leafmost abundant protein on Earth
    8. 8. Phase 2: Reduction
    9. 9. Calvin Cycle: Energy UtilizationATP phosphorylateseach 3-carbonmoleculereaction type:phosphorylationenzyme: kinaseenergy: absorbed
    10. 10. Calvin Cycle: Energy UtilizationNADPH used tosynthesize G3Preaction type: redoxenzyme:dehydrogenaseenergy: absorbed
    11. 11. Phase 3: RegenerationOf the 6 G3P produced 1 of them exits thecycle to eventually become glucose andother types of organic compoundsThe other 5 G3P continue in the cycle to helpregenerate the starting substances
    12. 12. Phase 3: Regeneration
    13. 13. Calvin Cycle: RegenerateMoleculesG3P resynthesized to 1,5-RuBP5 x 3C (G3P)  3 x 5C(RuBP)15 C in totalUses ATPreaction type: synthesisenzyme: synthaseenergy: absorbed
    14. 14. Adaptations to LimitationsPhotorespiration limitations:C3 plantAdaptations to hot, arid conditions:C4 plantsCAM plants
    15. 15. C3 PlantsPlants whosefirst organicproduct ofcarbon fixationis a 3-carboncompoundC3 plantsundergophotosynthesisas described(3-PGA or PGA or 3PG)
    16. 16. C3 PlantsStomata are openduring the day /closed at nightWhat happens tostomata in hot,arid conditions?
    17. 17. Stomata
    18. 18. C3 Plant LimitationsIn hot, aridconditions,plants close thestomata toprevent waterlossWhat affectdoes that haveon CO2 and O2concentration?
    19. 19. C3 Plant LimitationsClosed stomata CO2 decreases:Slows/stops Calvin cycleClosed stomata O2 increases:rubisco binds to O2 rather than CO2skip the Calvin cycleglucose is not produced
    20. 20. Rubisco2 possible substrates: CO2 or O2Carboxylase: binds CO2 yields 2x PGAOxygenase: binds O2 yields 1x PGA and PG
    21. 21. Rubisco Reaction
    22. 22. Phosphoglycollate (PG)cannot be converted directly into sugarsis a wasteful loss of carbonto retrieve the carbon from it, plants mustuse an energy-expensive processcalled photorespiration
    23. 23. Photorespiration (aka photo-oxidation)“photo”: occurs in the lightunlike photosynthesis, produces no organic fuel(no Calvin cycle)“respiration”: consumes oxygen (by rubisco)unlike cellular respiration, generates no ATPwastes energy and reducing powerresults in the production of dangerousreactive oxygen species (H2O2) in theperoxisome
    24. 24. Why does photorespiration exist?Evolutionary baggage:Metabolic relic from earlier time whenatmosphere had less O2 and more CO2With so much CO2, rubisco’s inability to excludeO2 had little impact on photosynthesisModern times:Rubisco’s affinity for O2 has a negative impact oncrop yields
    25. 25. C3 Plants: Agricultural CropsHot arid dry conditions are detrimental to C3 plantsThese conditions have a negative impact for farmersand consumers of C3 agricultural crops: rice, wheat, soy
    26. 26. Evolutionary EfficiencyAtmospheric O2 is 500x higher than CO2Yet rubisco fixes on average 4 CO2 for everyO2
    27. 27. Photosynthetic Adaptations2 other plant types have adaptedphotosynthesis to dry, arid conditions:C4 plants – spatial (structural) separationCAM plants – temporal (behavioural) separation
    28. 28. PEP CarboxylaseVery high affinity for CO2Can fix carbon even when CO2 levelsdecrease and O2 levels risePEP (3C) + CO2  OAA (4C)OAA  MalateMalate  pyruvate (3C) + CO2Pyruvate  PEP
    29. 29. C4 PlantsPreface the Calvin cycle with an alternate mode ofcarbon fixation that produces a 4-carbon compoundas their first organic productAgricultural C4 crops: sugar cane, corn
    30. 30. C4 Plant: Leaf StructureBundle-sheath cells tightlypacked around vascular bundleMesophyll cells looselyarranged near the leaf surface
    31. 31. C4 Plant AdaptationCalvin cycle confined tobundle-sheath cellsPreceded by incorporatingCO2 into organic compoundsin the mesophyll
    32. 32. C4 Plant AdaptationCO2 added to a 3-carbonphosphoenolpyruvate (PEP)to form a 4-carbonoxaloacetate (OAA)
    33. 33. C4 Plant Adaptation4C compound is exportedto bundle-sheath cellswhere it releases CO2 anda 3C pyruvateCO2 is assimilated into theCalvin cycle by rubiscoPyruvate returns to themesophyll cell to beconverted back to PEP (3C)
    34. 34. C4 Plant AdaptationMesophyll cells act as aCO2 pumpKeeps concentration ofCO2 in bundle-sheath cellshigh (and oxygen low) sothat rubisco can bind CO2
    35. 35. CAM PlantsCAM: Crassulacean acid metabolismSucculent (water-storing) plantsExample: cacti, pineapples
    36. 36. CAM Plant AdaptationNighttime:Stomata openTake up CO2 and added toa 3-carbon PEP to form a4-carbon OAAEnzyme: PEP carboxylaseFurther converted tomalate (malic acid) whichis stored in vacuoles ofmesophyll cells
    37. 37. CAM Plant AdaptationDaytime:Stomata closedConserve waterno CO2 uptakeLight reactions makeATP and NADPHCO2 in organic acidstored in vacuoles fromthe night is released torun the Calvin cycle
    38. 38. CAM Plant Adaptation
    39. 39. CAM Plant AdaptationNighttime: CO2incorporation intoorganic acids,stored in vacuoleDaytime: Calvincycle with energyfrom light reactionand CO2 fromnight storage
    40. 40. C4 and CAM PlantsCO2 is incorporated into organic intermediatesbefore entering Calvin cycleC4: initial carbon fixation separated structurallyCAM: initial carbon fixation separated temporally
    41. 41. Factors AffectingPhotosynthesisLight intensityCarbon dioxide concentrationTemperature
    42. 42. Light Intensity Low-mid intensity: linearresponse Higher intensity: saturationdue to other limitingfactors in photosynthesis Highest intensity:photorespiration light compensation point:minimum light intensity atwhich the leaf shows a netgain of carbon intensityRateofPhotosynthesisPhoto-respiration
    43. 43. Light Intensityfactors contributing to saturationRate at whichphotosynthesisis saturated isincreased withtemperatureand CO2 levels
    44. 44. CO2 ConcentrationsLow concentration:CO2 diffusion limitsrateHigh concentration:saturation due to otherlimiting factors inphotosynthesis concentrationRateofPhotosynthesis
    45. 45. CO2 Concentrationsfactors contributing to saturationRate at whichphotosynthesis issaturated isincreased withlight intensity
    46. 46. TemperatureEach type ofplant has atemperaturerange wherephotosynthesisis optimal coastaldune plantEvergreendesert shrubSummer-active desertperennial
    47. 47. Temperaturefactors contributing to maximum rate of photosynthesisIncreased CO2levels increasesthe maximal rateof photosynthesis
    48. 48. Photosynthesis Rate FactorsFactor Effect on Rate of photosynthesisLightintensityLightreactionsIncrease to a plateau(saturation) since Calvin cyclecannot keep up with lightreactionsCO2 levelsCalvincycleIncrease to a plateau sincelight reactions can not keepup with Calvin cycleTemperatureMaximum rate can beincreased by increasing CO2