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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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 - PowerPoint PPT Presentation

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Page 1: Calvin Cycle

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

Page 2: Calvin Cycle

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

Page 3: Calvin Cycle

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

Page 4: Calvin Cycle

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

Page 5: Calvin Cycle

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

Page 6: Calvin Cycle

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

Page 7: Calvin Cycle

Calvin Cycle

3H2O

2H2O

2 Pi

3RuBP+3CO2+9ATP+6NADPH+5H2O9ADP+8Pi+6NADP++G3P+3RuBP

Page 8: Calvin Cycle

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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