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

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

The Calvin Cycle Light independent reaction Occurs in Stroma of chloroplast ATP and NADPH from light reaction used to reduce CO 2 into carbohydrate molecules Divided into 3 stages 1. Carbon Fixation 2. Reduction reactions 3. Ribulose 1,5-bisphosphate (RuBP) regeneration

Phase 1: Carbon Fixation CO 2 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 CO 2 are used and 6 PGA are produced ogy/Bio231/calvin.html

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 ogy/Bio231/calvin.html

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 CO 2 in the next cycle gy/Bio231/calvin.html

Calvin Cycle  3H 2 O 2H 2 O  2 Pi  3RuBP+3CO 2 +9ATP+6NADPH+5H 2 O  9ADP+8P i +6NADP + +G3P+3RuBP

To Produce One G3P… 3 RuBP + 3 CO ATP + 6 NADPH + 5 H 2 O  9 ADP + 8 P i + 6 NADP + + G3P + 3 RuBP hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535 ::/sites/dl/free/ /120072/bio13.swf::Ph otosynthetic%20Electron%20Transport%20and%20 ATP%20Synthesis Tutorial 8.3 Tracing the Pathway of CO2