This preview shows page 1. Sign up to view the full content.
Unformatted text preview: to PSI Dual roles of cytochrome b6f and cytochrome c6 in cyanobacteria Ferredoxin-NADP+ reductase (FNR) NADP+ FAD Segragation of PSI and PSII Photophosphorylation
• Light-driven electron transport generates a proton gradient, which powers the enzymatic synthesis of ATP by the chloroplast ATP synthase (the CF1CF0 complex) in a manner similar to the oxidative phosphorylation • ~ 12 protons enter the lumen per molecules of O2 produced by the noncyclic electron transport, which theoretically produces ~ 3 ATPs 2 H2O + 8 photons + 2 NADP+ + ~ 3 ADP + ~ 3 Pi → O2 + ~ 3 ATP + 2 NADPH Summary of the light reactions Topology of proton movement and ATP synthase orientation Assimilation of CO2 into biomass in plants Three stages of CO2 assimilation (the Calvin cycle or the C3 pathway) The structure of ribulose 1,5-bisphosphate carboxylase (Rubisco) The first stage of CO2 assimilation The second stage of CO2 assimilation The third stage of CO2 assimilation Stoichiometry of CO2 assimilation in the Calvin cycle
3 CO2 + 9 ATP + 6 NADH → GAP + 9 ADP + 8 Pi + 6 NADP+ Sucrose synthesis Starch synthesis Photorespiration (the oxidative photosynthetic carbon cycle or C2 cycle)
• At low CO2 and high O2 levels, illuminated C3 plants consume O2 and evolve CO2 by photorespiration Results from Rubisco’s oxygenase activity The salvage of phosphoglycolate is wasteful because ATP and NADPH are uselessly dissipated Possibly protects the photosynthetic apparatus from photooxidative demage when insufficient CO2 is available In C4 plants (many tropical plants), CO2 fixation and Rubisco activity are spatially separated, almost totally preventing photorespiration In CAM plants, CO2 capture (night) and Rubisco action (morning) are temporally separated • • • • • Oxygenase activity of Rubisco The C4 pathway...
View Full Document