Dark reaction in stroma compartment(The dark reaction depends on light)In the dark, plants actually use the pentose phosphate pathway, glycolysis, Krebs cycle and oxidativecycle, and oxidative phosphorylation for ATP and NADPH synthesis. These pathways are also used during the day for energy productionthe day for energy production. Most of the ATP and NADPH in chloroplasts is used for carbon fixation, not for general use in the rest of the celluse in the rest of the cell. energy is exported as carbohydrates into the cytoplasm or stored as starch in the stromaCalvin Cyclein the stroma.Fig20-34, Cox, LehningerVoet, Fundamentals, 3rdFig. 19.25Net synthesis of a triose unitFig20-30, Cox, LehningerStarch synthesis via acti ated ADPgl coseactivated ADP-glucoseVoet, Fundamentals, 3rdFig. 19.29Sucrose synthesis via activated UDP-glucoseygPage 669Voet, Fundamentals, 3rdUse and storage of carbohydrates synthesized in chloroplastsFig20-25, Cox, LehningerRegulation of Calvin cycleegu at o o Cacyc eKey regulatory steps via redox potential :potential :Fructos-1,6-biphosphataseSedoheptulose-17-biphosphataseSedoheptulose-1,7-biphosphatasePhospho-ribulose kinaseGlyceraldehyde 3-phosphateGlyceraldehyde 3phosphate dehydrogenaseVoet, Fundamentals, 3rdFig. 19.26Voet, Fundamentals, 3rdLight-activation mechanism of FBPase and SBPase.Redox potential (availability of NADPH as measured by Ferredoxing concentration) controls:Fructos16biphosphataseFructos-1,6-biphosphataseSedohyeptulose-1,7-biphosphataseRibulose-5-phosphate kinaseGlyceraldehyde 3-phosphate dehydrogenase(reductive step)(reductive step)Voet, Fundamentals, 2nd Fig. 19.30pH sensitivity of fructose-1,6-biphosphatase in stromaDuring light reaction, the stroma compartment becomes alkaline at the expense of proton pumping into thylakoid lumen. Low H+concentration is compensated by Mg++antiport; Mg++catalyzes CO2dependent Rubisco carbamation, which ti t thi kactivates this key enzymeFig20-36, Cox, LehningerPhotorespiration oto esp at oVoet, Fundamentals, 3rdFig. 19.32Increasing CO2 concentration in C4 plants to reduce O2p2inhibition of RUBISCOVoet, Fundamentals, 3rdFig. 19.33Reductive carboxylate cycle in photosynthetic microorganismsEl tEl tElectron sourceElectron sourceA 3-Hydroxypropionate/4-Hydroxybutyrate Autotrophic Carbon Dioxide Assimilation PathwayAutotrophic Carbon Dioxide Assimilation Pathway in ArchaeaNet reactions:Acetyl-CoA + 2CO2= Succinyl-CoASuccinylCoA is further reduced and splitSuccinyl-CoA is further reduced and split into 2 Acetyl-CoABerg, I. A., D. Kockelkorn, et al. (2007). Science 318(5857): 1782-1786.The glyoxylate cycle in plants, bacteria and fungi can make carbohydrates from acetyl-CoAAcetyl-CoA from fatty acid degradation in glyoxysomeVoet, Fundamentals,
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