Metabolites of the Calvin CycleThese ATP andNADPH moleculeswere produced bythe light reactions.3 ADP + 3P6 ADP + 6PThese ATPmolecules wereproduced by thelight reactions.net gain of one G3PGlucoseCO2fixationCO2reductionregenerationof RuBPintermediate6 NADPH+5 G3PC33 RuBPC56 G3PC36 BPGC33 CO2Other organic molecules6 NADPH3ATP6ATPCalvin cycle6 3PGC33 C6CH2OstromaH2OCO2ADP+PNADPHNADP+ATPO22solarenergyLightreactionsCalvincycleFrom our text -
Calvin Cycle Reactions: Carbon Dioxide ReductionNADPHNADP+ATP3PGG3PBPGADP +PAs 3PG becomes G3P, ATP becomesADP +and NADPH becomes NADP+P3PG is reduced to BPGBPG is then reduced to G3PUtilizes NADPH and some ATP produced in the light reactions
Calvin Cycle Reactions: Regeneration of RuBPAs five molecules of G3P become threemolecules of RuBP, three molecules of ATPbecome three molecules of ADP +3 ATP5 G3P3 RuBP3 ADP +PPRuBP used in CO2fixation must be replacedEvery three turns of Calvin Cycle,Five G3P (a 3-carbon molecule) are used (5 x 3 = 15 C)To remake three RuBP (a 5-carbon molecule) (3 x 5 = 15 C)5 X 3 = 3 X 5
Importance of the Calvin CycleG3P (glyceraldehyde-3-phosphate) can be converted to many other moleculesThe hydrocarbon skeleton of G3P can formFatty acids and glycerol to make plant oilsGlucose phosphate (simple sugar)Fructose (which with glucose = sucrose)Starch and celluloseAmino acids
C4PhotosynthesisIn hot, dry climatesStomata must close to avoid wiltingCO2decreases and O2increasesO2starts combining with RuBP, leading to the production of CO2Called photorespirationC4plants solve the problem of photorespirationFix CO2to PEP (a C3molecule)The result is oxaloacetate, a C4moleculeIn hot & dry climatesC4plants avoid photorespirationNet productivity is about 2-3 times greater than C3plantsIn cool, moist environments, C4plants can’t compete with C3 plants
Photosynthesis – C4pathway•CO2
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