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- 1. Open EndedThe Calvin cycle consists of three stages.
- 2. Open EndedRibulose 1,5 bisphosphate is carboxylated and cleaved by rubisco to produce 2 molecules of 3 phosphoglycerate. Phosphoglycerate kinase (using ATP) and 1,3 bisphosphoglycerate dehydrogenase (using NADPH) produce glyceraldehyde 3-phosphate - this can then be converted into glucose via gluconeogenic enzymes. Stage 3 is the regeneration of our original acceptor molecule ribulose 1,5 bisphosphate For the net formation of one molecule of glyceraldehyde 3 phosphate, we need to fix 3 molecules of CO2 So: 3 molecules of ribulose 1,5 bisphosphate (3x 5 carbons = 15 carbons total) accept 3 molecules of CO2 to generate 6 molecules of 3 phosphoglycerate (3 x 6 carbons = 18 carbons total) These 6 molecules of 3 phosphoglycerate are reduced to 6 molecules of glyceraldehyde 3 phosphate = 18 carbons total. ONE of these molecules of glyceraldehyde 3 phosphate can now be syphoned off into glucose synthesis = 3 carbons total The remaining 5 molecules of glyceraldehyde 3 phosphate are used to regenerate the 3 molecules of ribulose 1,5 bisphosphate we had at the start of the cycle. This means that 3 complete turns of the cycle result in the net formation of one molecule of glyceraldehyde 3 phosphate, So 6 turns of the Calvin cycle are needed to make one molecule of glucose
- 3. Open EndedStage 1. Fixation of CO2 by ribulose 1,5-bisphosphate to form two molecules of 3-phosphoglycerate
- 4. Open EndedRubisco is perhaps the most abundant enzyme on Earth (and also one of the least efficient)
- 5. Open EndedStage 2: 3-phosphoglycerate Reduced to Glyceraldehyde 3-Phosphate
- 6. Open EndedRegeneration of ribulose 1,5-bisphosphate
- 7. Open EndedThe fixed carbons from photosynthesis have two principle fates:
- 8. Open EndedThe Calvin cycle is regulated by the environment
- 9. Open EndedThioredoxin plays a key role in regulating the Calvin Cycle
- 10. Open EndedReduced thioredoxin activates certain Calvin-cycle enzymes by cleaving regulatory disulfide bonds.
- 11. Open EndedPhotorespiration is a wasteful side reaction of Rubisco
- 12. Open EndedIn tropical plants the C4 pathway reduces photorespiration and accelerates photosynthesis
- 13. Open EndedThe C4 pathway
- 14. Open EndedCrassulacean Acid Metabolism permits growth in arid ecosystems
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