Processes affected by pCO 2 Pathways that use CO 2 as substrate
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Processes affected by pCO2
1)Pathways that use CO2 as substrate• Calvin cycle (Carbon reduction pathway)
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Processes affected by pCO2
1)Pathways that use CO2 as substrate• Calvin cycle (Carbon reduction pathway)
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Processes affected by pCO2
Calvin cycle (Carbon reduction pathway)1)RuBP binds CO2 2) rapidly splits into two 3-Phosphoglycerate
• therefore called C3 photosynthesis
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Processes affected by pCO2
Calvin cycle (Carbon reduction pathway)1)RuBP binds CO2 2) rapidly splits into two 3-Phosphoglycerate3) catalyzed by Rubisco (ribulose 1,5 bisphosphate carboxylase/oxygenase)the most important & abundant protein on earth
•Lousy Km
•Rotten Vmax!
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Processes affected by pCO2
Calvin cycle (Carbon reduction pathway)Reversing glycolysisconverts 3-Phosphoglycerate to G3Pconsumes 12 ATP & 12 NADPH/glucose
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Processes affected by pCO2
Calvin cycle (Carbon reduction pathway)Reversing glycolysisG3P has 2 possible fates
1) 1 in 6 becomes (CH2O)n
2) 5 in 6 regenerate RuBP
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Processes affected by pCO2
5 in 6 G3P regenerate RuBPBasic problem: converting a 3C to a 5C compoundfeed in five 3C sugars, recover three 5C sugars
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Regenerating RuBPBasic problem: converting a 3C to a 5C compoundmust assemble intermediates that can be broken into 5 C sugars after adding 3C subunit
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Processes affected by pCO2
1)Pathways that use CO2 as substrate•Calvin cycle (Carbon reduction pathway)• Rubisco must be carbamylated & bind Mg2+ to be active!
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Processes affected by pCO2
1)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
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Processes affected by pCO2
1)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)
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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
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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
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Processes affected by pCO2
Demand is set by mesophyll, stomata control supplyCi is usually much lower than Ca
A vs Ci plots tattle on the Calvin cycle
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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
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Processes affected by pCO2
Currently Rubisco usually limits C3 plantsWill increase plant growth until hit new limiting factor
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Processes affected by pCO2
Currently Rubisco usually limits C3 plantsWill increase plant growth until hit new limiting factor Free-Air CO2 Enrichment Experiments show initial gains,
but taper off w/in a few yearsNow are limited by nutrients or water
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Processes affected by pCO2
Pathways that use CO2 as substrate•Calvin cycle (Carbon reduction pathway)•Carbonic anhydrase: used to increase Cp CO2
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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)
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Processes affected by pCO2
1)Pathways that use CO2 as substrate• Calvin cycle (Carbon reduction pathway)• Fatty acid synthesis
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Processes affected by pCO2
1)Pathways that use CO2 as substrate• Calvin cycle (Carbon reduction pathway)• Fatty acid synthesis• Phosphoenolpyruvate carboxylase
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Processes affected by pCO2
1)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
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Processes affected by pCO2
1)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
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Processes affected by pCO2
1)Pathways that use CO2 as substrate• Calvin cycle (Carbon reduction pathway)• Fatty acid synthesis• PEP carboxylase• Pyruvate carboxylase (&/or malic enzyme)• gluconeogenesis
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Processes affected by pCO2
1)Pathways that use CO2 as substrate• Pyruvate carboxylase • PEPcarboxykinase• carbamoyl phosphate synthetase: pyrimidine synthesis & ornithine/urea cycle
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Processes affected by pCO2
1)Pathways that use CO2 as substrate2) Pathways that release CO2
• photorespiration: glycine decarboxylase
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Processes affected by pCO2
1)Pathways that use CO2 as substrate2) Pathways that release CO2
• photorespiration: glycine decarboxylase• Respiration (+ malic enzyme)
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Processes affected by pCO2
1)Pathways that use CO2 as substrate2) Pathways that release CO2
• Photorespiration• Respiration (+ malic enzyme)• CO2 Inhibits respiration at 3%• No obvious effects at 700 ppm, yet biomass reduced
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pathways that release CO2• Photorespiration• Respiration • Pentose phosphate shunt in cytosol or cp
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pathways that release CO2• Photorespiration• Respiration • Pentose phosphate shunt in cytosol or cp• Pyruvate decarboxylase in fermentation
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Pathways that release CO2• Serine or Phosphatidylserine decarboxylase for
ethanolamine, choline, etc synthesis
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Pathways that release CO2• Serine or Phosphatidylserine decarboxylase for ethanolamine, choline, etc synthesis• Aromatic Acid Decarboxylase for many precursors
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Pathways that release CO2• Serine or Phosphatidylserine decarboxylase for ethanolamine, choline, etc synthesis• Aromatic Acid Decarboxylase for many precursors• Many more AA Decarboxylases
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Processes affected by CO2
2) pathways that release CO2
3) transpiration & stomatal number