Calvin Cycle
Calvin Cycle Overview
Calvin cycle is a cyclical process which:
1. Fixes carbon (make C-C bonds)
2.

Utilizes energy molec...
Calvin Cycle
occurs in the stroma

of chloroplast

reactions are not as

linear as Krebs
Calvin Cycle: Carbon Fixation
1. three CO2 (1 carbon)

are attached to three
1,5-ribulose
bisphosphate (5
carbon)
rxn type...
Rubisco
ribulose bisphosphate carboxylase / oxygenase
large, slow reacting enzyme
most enzymes process 1000 reactions / ...
Calvin Cycle: Energy Utilization
ATP phosphorylates each
3-carbon molecule
rxn type: phosphorylation
enzyme: kinase
energy...
Calvin Cycle: Energy Utilization
NADPH used to
synthesize G3P
rxn type: redox
enzyme: dehydrogenase
energy: absorbed
Calvin Cycle: Regenerate Molecules
1.

5 G3P and ATP to
resynthesize 1,5-ribulose
bisphosphate

2.

1 G3P used in another
...
Calvin Cycle Review
1. 6 CO2 molecules are fixed to form a single glucose

molecule
2. 18 ATP & 12 NADPH molecules used
3....
Factors Overview
1. light intensity, [CO2] and temperature
2. C3 plant limitations
3. C4 plants
4. CAM plants
Photosynthesis Rate

Photosynthesis Rate
Photosynthesis Rate Factors
1. increased [CO2] = increased photosynthesis
2. increased temperature = increased photosynthe...
C3 Plant Limitations
C3 plants undergo
photosynthesis as
described
stomata are open
during the day /
closed at night
What ...
C3 Plant Limitations
In hot, arid conditions, plants close the stomata and
increases [O2] within the cells.
At high [O2], ...
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.
1. Mesophyll cells create 4-ca...
CAM Plant Adaptation
adaptation to hot, arid environments
e.g. cactus, pineapples (water storing plants)
Stomata are cl...
CAM Plant Adaptation
1. CO2 collected & incorporated into organic

molecules at night
2. CO2 released from the organic mol...
Tang 07 calvin cycle-plant limitations
Tang 07 calvin cycle-plant limitations
Tang 07 calvin cycle-plant limitations
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Tang 07 calvin cycle-plant limitations

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Tang 07 calvin cycle-plant limitations

  1. 1. Calvin Cycle
  2. 2. Calvin Cycle Overview Calvin cycle is a cyclical process which: 1. Fixes carbon (make C-C bonds) 2. Utilizes energy molecules 3. Regenerates molecules for another cycle
  3. 3. Calvin Cycle occurs in the stroma of chloroplast reactions are not as linear as Krebs
  4. 4. Calvin Cycle: Carbon Fixation 1. three CO2 (1 carbon) are attached to three 1,5-ribulose bisphosphate (5 carbon) rxn type: synthesis & cleavage enzyme: synthase & lyase (Rubisco) energy: absorbed 2. three 6-carbon molecule are split into six 3-carbon molecules
  5. 5. 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 for Calvin cycle half the protein in a leaf most abundant protein on Earth
  6. 6. Calvin Cycle: Energy Utilization ATP phosphorylates each 3-carbon molecule rxn type: phosphorylation enzyme: kinase energy: absorbed
  7. 7. Calvin Cycle: Energy Utilization NADPH used to synthesize G3P rxn type: redox enzyme: dehydrogenase energy: absorbed
  8. 8. Calvin Cycle: Regenerate Molecules 1. 5 G3P and ATP to resynthesize 1,5-ribulose bisphosphate 2. 1 G3P used in another pathway rxn type: synthesis phosphorylation enzyme: synthase kinase energy: absorbed
  9. 9. Calvin Cycle Review 1. 6 CO2 molecules are fixed to form a single glucose molecule 2. 18 ATP & 12 NADPH molecules used 3. electrons from 10 H2O transferred through the light reactions
  10. 10. Factors Overview 1. light intensity, [CO2] and temperature 2. C3 plant limitations 3. C4 plants 4. CAM plants
  11. 11. Photosynthesis Rate Photosynthesis Rate
  12. 12. Photosynthesis Rate Factors 1. increased [CO2] = increased photosynthesis 2. increased temperature = increased photosynthesis 3. increased light intensity = increased photosynthesis  only to a certain plateau since Calvin cycle cannot keep up with the light reactions
  13. 13. 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?
  14. 14. C3 Plant Limitations In hot, arid conditions, plants close the stomata and increases [O2] within the cells. At high [O2], rubisco binds to O2 rather than CO2 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
  15. 15. C4 Plant Adaptation adaptation to hot, arid environments e.g. corn, sugarcane, grasses
  16. 16. C4 Plant Adaptation C4 plants have a special mesophyll cell & bundle-sheath cell structure. 1. Mesophyll cells create 4-carbon molecules using PEP carboxylase and release CO2 into the bundle-sheath cells. 2. Bundle-sheath cells only perform the Calvin cycle. In hot, arid conditions, C4 cells provide enough CO2 to ensure rubisco does not bind to O2 molecules.
  17. 17. CAM Plant Adaptation adaptation to hot, arid environments e.g. cactus, pineapples (water storing plants) Stomata are closed in the day and open at night.
  18. 18. CAM Plant Adaptation 1. CO2 collected & incorporated into organic molecules at night 2. CO2 released from the organic molecules during the day where ATP & NADPH is produced to allow the Calvin cycle to proceed

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