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BIO 201 - Cell BiologyDr. Lara HutsonLecture 24 Photosynthesis: Calvin CycleMarch 31, 20141

An average person at rest will consume his or her weight in ATP in 24 hrs.OverviewThe Calvin CycleOverview of plant metabolism

2The reactions of photosynthesis (cont.)3

Calvin Cycle reactions take place in the chloroplast stroma.The Calvin Cycle: Making sugar from CO2 using the chemical energy from ATP and NADPH4Carbon fixationReduction reactionsRegeneration of RuBP(credit: thirdeyemax.com

G3P + ADP + Pi + NADP+CO2 + ATP + NADPHSimplified net reactions:(3C)Mostly transported out of the chloroplast to make glucose and other sugarsFollowing carbon in the Calvin Cycle5

Flask of algaeAdd CO2 containing 14C to flask containing algae.Wait short time.Extract small molecules.Use 2D chromatography to separate molecules based on size and chemical properties

Following carbon in the Calvin Cycle6

3 sec30 sec*

*3PG = 3 phosphoglycerate (3C)The first step of the Calvin Cycle: Carbon fixation7

*3-phosphoglycerate (3PG)Catalyzed by RubiscoCO2 binds to RuBP (5C). The resulting 6C sugar is immediately converted to 2 molecules of 3PG (3C).3-phosphoglycerate (3PG)*Rubisco is thought to be the most abundant protein in the world!

7The Calvin Cycle8

ATP and NADPH consumed during reduction reactions.RuBP must be regenerated in order for carbon fixation to continue. This uses more ATP.10 G3P used to regenerate 6 RuBP.2 of 12 glyceraldehyde-3-phosphate (G3P) used to make glucose and other sugars.Numbers based on production of 1 molecule glucose.Summary of photosynthetic reactions9Light-dependent reactions:2 G3P + 6 O26 CO2 + 6 H2ONet reactions of photosynthesis:Calvin Cycle:ATP + NADPH + O2Sunlight + ADP + Pi + NADP+ + H2OG3P + ADP + Pi + NADP+CO2 + ATP* + NADPH*Remember: The amount of ATP produced for every NADPH in the non-cyclic light-dependent reactions is not sufficient for the Calvin Cycle, so some ATP is also produced in the cyclic reactions.With glucose synthesis:C6H12O6 + 6 O26 CO2 + 6 H2OSummary of plant metabolism10

LIGHT-DEPENDENT REACTIONSNADPH, ATPETSATP,NADH, FADH2ATP,NADHATPPlant CellChloroplastMitochondrionSummary11The Calvin Cycle reactions use the energy from ATP and NADPH to reduce CO2 to G3P.Carbon fixation is catalyzed by Rubisco.Only 1 in 6 G3P molecules is used to make sugars.The other 5 are used to regenerate RuBP.Photosynthesis is used to generate sugars and precursors to other compounds.Aerobic metabolism is functional and produces ATP for other processes.