Download - Calvin Cycle
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Calvin Cycle• Chemical energy captured in ATP
and NADPH is used to “fix” carbon dioxide in the dark reaction
• 5C sugar + CO2 _ 2 x 3C sugars • CO2 is fixed into a 3 carbon sugar • Referred to as C3 photosynthesis • The enzyme that catalyzes this
reaction is called ribulose bisphosphate carboxylase, or rubisco
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Importance of Calvin Cycle
• Removes 200 billion tons of CO2 from the air every year
• Rubisco is the most abundant protein on earth, 20 kgs for every human
• When forests are cut down and cleared, some of this capacity to remove CO2 from the atmosphere is lost, contributing to global warming and the greenhouse effect
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The Calvin CycleThe Calvin Cycle•Light independent reaction
•Occurs in Stroma of chloroplast
•ATP and NADPH from light reaction used to reduce CO2 into carbohydrate molecules
•Divided into 3 stages
1. Carbon Fixation
2. Reduction reactions
3. Ribulose 1,5-bisphosphate (RuBP) regeneration
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Phase 1: Carbon Fixation
• CO2 joins to RuBP (5C) to form a 6C intermediate
• This reaction is catalyzed by enzyme rubisco• Intermediate 6C molecule immediately splits into two 3C
molecules called PGA (3-phosphoglycerate)
• This reaction occurs 3 times, therefore 3 CO2 are used and 6 PGA are produced
http://www.science.smith.edu/departments/Biology/Bio231/calvin.html
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Phase 2: Reduction Reactions
• 6 PGA molecules are phosphorylated by ATP to produce 6 molecules of 1,3-bisphophoglycerate (1,3 BPG)
• 6 1,3 BPG are then reduced by NADPH to produce 6 glyceraldehyde 3-phosphate (G3P) – a sugar
• One G3P exits the cycle as a final product and the remaining 5 G3P are used in RuBP regeneration
• G3P that exited is used to synthesize larger sugars
http://www.science.smith.edu/departments/Biology/Bio231/calvin.html
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Phase 3: RuBP Regeneration
• 5 G3P are rearranged to form 3 molecules of RuBP• 3 ATP are used in this process
• The RuBP is now available to join with the next CO2 in the next cycle
http://www.science.smith.edu/departments/Biology/Bio231/calvin.html
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Calvin Cycle
3H2O
2H2O
2 Pi
3RuBP+3CO2+9ATP+6NADPH+5H2O9ADP+8Pi+6NADP++G3P+3RuBP
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To Produce One G3P…
3 RuBP + 3 CO2 + 9 ATP + 6 NADPH + 5 H2O 9 ADP + 8 Pi + 6 NADP+ + G3P + 3 RuBP
http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120072/bio13.swf::Photosynthetic%20Electron%20Transport%20and%20ATP%20Synthesis
Tutorial 8.3 Tracing the Pathway of CO2
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