Calvin Cycle (Calvin-BensonCycle)
• Melvin Calvin
• Used radioisotope14CO 2
○ Tracer experiments
○ Mapped the route of CO during photosynthesis
Trivial – take a few CO2, add water and get some glucose!???
How Is Carbon Dioxide Reduced to Produce (Glucose/Sucrose)Triose-P?
• light-dependent reactions & CO re2uction of the Calvin cycle
○ two separate but linked processes in photosynthesis
• ATP and NADPH are produced by photosystemsI and II in presence of light
• The reactions producing sugar from CO in2the Calvin cycle are light-independent
• The Calvin cycle reactions can occur in the dark, BUT require ATP and NADPH produced by
light dependent reactions
Carbon dioxide is reduced in 3 Phases in the Calvin Cycle in the stroma of the chloroplast
1 CO2 + ribulose bisphosphate (RuBP) -> 2 3-phosphoglycerate
Attachment of CO2 to an organic compound is called carbon fixation
2 3-phosphoglycerateare phosphorylated by ATP and reduced by NADPH -> 2 glyceraldehyde
Remaining G3P is used in reactions that regenerate RuBP G3P is the product of the Calvin Cycle
• 1 turn of the Calvin cycle fixes
1 molecule of CO2
• 3 turns of the Calvin cycle produce
1 molecule of G3P
Not glucose, sucrose or starch!
• Where do mono- and disacharides comefrom?
-> End product synthesis in subsequent reactions
Endproduct synthesis: Sucrose and starch are the main products of photosynthesis
Synthesis of starch & sucrose from triose-p derived from photosynthesis
• Export of G3P moleculesfrom Calvin cycle to cytosol:
○ glucose, fructose, -> sucrose.
• Rapidly photosynthesizing cells accumulate glucos