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Processes affected by pCO 2 Pathways that use CO 2 as substrate

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

melinda-rowe
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Processes affected by pCO 2 Pathways that use CO 2 as substrate

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  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 five3C sugars, recover three5C 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 orcp

  30. pathways that release CO2 • Photorespiration • Respiration • Pentose phosphate • shunt in cytosol orcp • 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

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