Outline the three main stages of the Calvin cycle: • rubisco catalyses the fixation of carbon dioxide by combination with a molecule of ribulose bisphosphate (RuBP), a 5C compound, to yield two molecules of glycerate 3-phosphate (GP), a 3C compound • GP is reduced to triose phosphate (TP) in reactions involving reduced NADP and ATP • RuBP is regenerated from TP in reactions that use ATP

SouravNovember 1, 2024

Answer

The Calvin cycle consists of three main stages:

1. Carbon Fixation
   • Enzyme Rubisco catalyzes the reaction between carbon dioxide and ribulose bisphosphate (RuBP), a five-carbon (5C) molecule.
   • This reaction produces an unstable six-carbon intermediate, which immediately splits into two molecules of glycerate 3-phosphate (GP), each containing three carbons (3C).
2. Reduction
   • Glycerate 3-phosphate (GP) is reduced to form triose phosphate (TP), a three-carbon molecule.
   • This reduction requires ATP and reduced NADP (both products of the light-dependent reactions of photosynthesis).
   • NADPH donates electrons, while ATP provides energy for the reduction of GP to TP.
3. Regeneration of RuBP
   • Some of the triose phosphate (TP) molecules are used to regenerate ribulose bisphosphate (RuBP), enabling the cycle to continue.
   • This regeneration process also requires ATP to drive the reactions.
   • The remaining TP can be used to form glucose and other organic molecules.

These three stages allow the Calvin cycle to fix carbon, synthesize sugars, and regenerate the initial molecule RuBP, thereby supporting continuous carbon fixation and sugar production in plants.