1. Processes affected by pCO2
Pathways that use CO2 as substrate
Calvin cycle (Carbon reduction pathway)

2. Processes affected by pCO2
Pathways that use CO2 as substrate
Calvin cycle (Carbon reduction pathway)

3. Processes affected by pCO2
Calvin cycle (Carbon reduction pathway)
RuBP binds CO2
2) rapidly splits into two 3-Phosphoglycerate
therefore called C3 photosynthesis

4. Processes affected by pCO2
Calvin cycle (Carbon reduction pathway)
RuBP binds CO2
2) rapidly splits into two 3-Phosphoglycerate
3) catalyzed by Rubisco (ribulose 1,5 bisphosphate carboxylase/oxygenase)
the most important &
abundant protein on earth
Lousy Km
Rotten Vmax!

5. Processes affected by pCO2
Calvin cycle (Carbon reduction pathway)
Reversing glycolysis
converts 3-Phosphoglycerate to G3P
consumes 12 ATP & 12 NADPH/glucose

6. Processes affected by pCO2
Calvin cycle (Carbon reduction pathway)
Reversing glycolysis
G3P has 2 possible fates
1) 1 in 6 becomes (CH2O)n
2) 5 in 6 regenerate RuBP

7. Processes affected by pCO2
5 in 6 G3P regenerate RuBP
Basic problem: converting a 3C to a 5C compound
feed in five 3C sugars, recover three 5C sugars

8. Regenerating RuBP
Basic problem: converting a 3C to a 5C compound
must assemble
intermediates that
can be broken into
5 C sugars after
adding 3C subunit

9. Processes affected by pCO2
Pathways that use CO2 as substrate
Calvin cycle (Carbon reduction pathway)
Rubisco must be carbamylated & bind Mg2+ to be active!

10. Processes affected by pCO2
Pathways that use CO2 as substrate
Calvin cycle (Carbon reduction pathway)
Rubisco must be carbamylated & bind Mg2+ to be active!
RuBP binds & inactivates uncarbamylated rubisco

11. Processes affected by pCO2
Pathways that use CO2 as substrate
Calvin cycle (Carbon reduction pathway)
Rubisco must be carbamylated & bind Mg2+ to be active!
RuBP binds & inactivates uncarbamylated rubisco
Rubisco activase removes this RuBP (also CA1P)

12. Processes affected by pCO2
rubisco usually limits C3 -> limited by demand for CO2
Supply is limited by resistance to CO2 diffusion
Boundary layer
Stomatal: only one
that can be adjusted
Liquid phase

13. Processes affected by pCO2
rubisco usually limits C3 -> limited by demand for CO2
Supply is limited by resistance to CO2 diffusion
Boundary layer
Stomatal: only one
that can be adjusted
Liquid phase
Demand is set by mesophyll,
Stomata control supply

14. Processes affected by pCO2
Demand is set by mesophyll, stomata control supply
Ci is usually much lower than Ca
A vs Ci plots tattle on the Calvin cycle

15. Processes affected by pCO2
A vs Ci plots tattle on the Calvin cycle
In linear phase rubisco is limiting
When curves RuBP or Pi regeneration is limiting

16. Processes affected by pCO2
Currently Rubisco usually limits C3 plants
Will increase plant growth until hit new limiting factor

17. Processes affected by pCO2
Currently Rubisco usually limits C3 plants
Will increase plant growth until hit new limiting factor
Free-Air CO2 Enrichment Experiments show initial gains, but taper off w/in a few years
Now are limited by nutrients or water

18. Processes affected by pCO2
Pathways that use CO2 as substrate
Calvin cycle (Carbon reduction pathway)
Carbonic anhydrase: used to increase Cp CO2

19. Processes affected by pCO2
Pathways that use CO2 as substrate
Calvin cycle (Carbon reduction pathway)
Carbonic anhydrase: used to increase Cp CO2
First step in C4 photosynthesis: PEPcase fixes HCO3-
also serves as CO2 sensor (mech unknown)

20. Processes affected by pCO2
Pathways that use CO2 as substrate
Calvin cycle (Carbon reduction pathway)
Fatty acid synthesis

21. Processes affected by pCO2
Pathways that use CO2 as substrate
Calvin cycle (Carbon reduction pathway)
Fatty acid synthesis
Phosphoenolpyruvate carboxylase

22. Processes affected by pCO2
Pathways that use CO2 as substrate
Calvin cycle (Carbon reduction pathway)
Fatty acid synthesis
Phosphoenolpyruvate carboxylase: plants often form malate cf pyr from glycolysis
Get more ATP/NADH

23. Processes affected by pCO2
Pathways that use CO2 as substrate
Calvin cycle
Fatty acid synthesis
Phosphoenolpyruvate carboxylase: plants often form malate cf pyr from glycolysis
Get more ATP/NADH
lets cells replace Krebs
intermediates used for synthesis
First step in C4

24. Processes affected by pCO2
Pathways that use CO2 as substrate
Calvin cycle (Carbon reduction pathway)
Fatty acid synthesis
PEP carboxylase
Pyruvate carboxylase
(&/or malic enzyme)
gluconeogenesis

25. Processes affected by pCO2
Pathways that use CO2 as substrate
Pyruvate carboxylase
PEPcarboxykinase
carbamoyl phosphate synthetase: pyrimidine
synthesis & ornithine/urea cycle

26. Processes affected by pCO2
Pathways that use CO2 as substrate
2) Pathways that release CO2
photorespiration: glycine decarboxylase

27. Processes affected by pCO2
Pathways that use CO2 as substrate
2) Pathways that release CO2
photorespiration: glycine decarboxylase
Respiration
(+ malic enzyme)

28. Processes affected by pCO2
Pathways that use CO2 as substrate
2) Pathways that release CO2
Photorespiration
Respiration
(+ malic enzyme)
CO2 Inhibits
respiration at 3%
No obvious effects
at 700 ppm, yet
biomass reduced

29. pathways that release CO2
Photorespiration
Respiration
Pentose phosphate shunt in cytosol or cp

30. pathways that release CO2
Photorespiration
Respiration
Pentose phosphate
shunt in cytosol or cp
Pyruvate decarboxylase
in fermentation

31. Pathways that release CO2
Serine or Phosphatidylserine decarboxylase for ethanolamine, choline, etc synthesis

32. Pathways that release CO2
Serine or Phosphatidylserine
decarboxylase for ethanolamine,
choline, etc synthesis
Aromatic Acid Decarboxylase
for many precursors

33. Pathways that release CO2
Serine or Phosphatidylserine
decarboxylase for ethanolamine,
choline, etc synthesis
Aromatic Acid Decarboxylase
for many precursors
Many more AA
Decarboxylases

34. Processes affected by CO2
2) pathways that release CO2
3) transpiration & stomatal number