the calvin cycle

• Energy from ATP and hydrogen from reduced NADP are passed from light dependent stage to the light independent stage of photosynthesis
• Energy and hydrogen are used during the light independent reactions ( known as Calvin cycle) to produce complex organic molecules including Carbohydrates such as

  • starch
  • sucrose
  • Cellulose
• Thee main steps:

  • Rubisco catalyzes the fixation of carbon dioxide by combination with a molecule of ribulose bisphosphate (RuBP) a 5 carbon compound, to yield two molecules of glycerate 3-phosphate (GP) a 3 carbon molecule
  • GP is reduced to triose phosphate (TP) in a reaction involving reduced NADP and ATP
  • RuBP is regenerated from TP in reactions that use ATP
• Carbon fixation:

  • Carbon dioxide combines with a 5 carbon (5c) sugar known as ribulose bisphosphate (RuBP)
• enzyme called rubisco catalyzes this reaction
• result 6c compound is unstable and splits in 2
• gives two molecules of 3 carbon molecule known as glycerate 3-phosphate (GP)
• carbon dioxide has been 'fixed' (removed from external environment and has become part of organic matter of the plant cell)
• Glycerate 3-phosplate (GP) is not a carbohydrate but the next step in calvin cycle converts it into one
• Reduction of Glycerate 3-phosphate

  1. Energy from ATP

  2. Hydrogen from reduced NADP

  3. Both produced during light-dependent stage of photosynthesis

  4. Used to reduce glycerate 3-phosphate (GP) to a phosphorylated 3c sugar known as triose phosphate (TP)
• Uses of triose phosphate (TP) molecules

  • 1/6 used to produce useful organic molecules needed by the plant
  • Condensed to become hexose phosphates (6C) which can be used to produce starch, sucrose, cellulose
  • Converted to glycerol and glycerate 3-phosphates to fatty acids which joins to form lipids for cell membranes
  • Used in the production of amino acids for protein synthesis
• Regeneration of Ribulose Bisphosphate

  • 5/6 of TP molecules are used to regenerate ribulose bisphosphate (RuBP)
  • Process requires ATP
• Diagram of Calvin cycle

  
• Calvin cycle intermediates

  • intermediate molecules of the Calvin cycle (such as glycerate 3-phosphate and triose phosphate) are used to produce some amino acids
  • TP is used to produce:
  • Hexose phosphates (6c): starch, sucrose or cellulose
  • Lipids for cell membranes
  • Amino acids for protein synthesis