The Calvin cycle
Overview of the Calvin cycle
Reactions of the Calvin cycle
- Regeneration. One G3P molecule leaves the cycle and will go towards making glucose, while five G3Ps must be recycled to regenerate the RuBP acceptor. Regeneration involves a complex series of reactions and requires ATP.
- Carbon fixation. A molecule combines with a five-carbon acceptor molecule, ribulose-1,5-bisphosphate (RuBP). This step makes a six-carbon compound that splits into two molecules of a three-carbon compound, 3-phosphoglyceric acid (3-PGA). This reaction is catalyzed by the enzyme RuBP carboxylase/oxygenase, or rubisco.
- Reduction. In the second stage, ATP and NADPH are used to convert the 3-PGA molecules into molecules of a three-carbon sugar, glyceraldehyde-3-phosphate (G3P). This stage gets its name because NADPH donates electrons to, or reduces, a three-carbon intermediate to make G3P.
- Regeneration. Some G3P molecules go to make glucose, while others must be recycled to regenerate the RuBP acceptor. Regeneration requires ATP and involves a complex network of reactions, which my college bio professor liked to call the "carbohydrate scramble."
Summary of Calvin cycle reactants and products
- Carbon. combine with RuBP acceptors, making molecules of glyceraldehyde-3-phosphate (G3P).
- G3P molecule exits the cycle and goes towards making glucose.
- G3P molecules are recycled, regenerating RuBP acceptor molecules.
- ATP. ATP are converted to ADP ( during the fixation step, during the regeneration step).
- NADPH. NADPH are converted to NADP (during the reduction step).