- The Calvin Cycle -
The Calvin Cycle involves the fixation and reduction of Carbon, Its as easy as 1,2,3.

1. Carbon is Fixed CO2 + RuBP -> 2 PGA molecules (1 + 5 = 2 X 3) Animation
2. The phosphoglyceric acid is reduced (using NADPH) to phosphoglyceraldehyde.
3. The fixed, reduced Carbon is rearranged to make Glucose and regenerate RuBP.

The Steps

  • CO2 combines with the phosphorylated 5-carbon sugar ribulose bisphosphate
  • This reaction is catalyzed by the enzyme ribulose bisphosphate carboxylase oxygenase (RUBISCO an enzyme which can fairly claim to be the most abundant protein on earth)
  • The resulting 6-carbon compound breaks down (real fast) into two molecules of
    3-phosphoglyceric acid     (PGA)
  • The PGA molecules are further phosphorylated (by ATP) and are reduced (by NADPH) to form phosphoglyceraldehyde (G3P, also called PGAL)
  • Phosphoglyceraldehyde serves as the starting material for the synthesis of glucose and fructose, or it can be used to make more RuBP.
  • Glucose and fructose make the disaccharide sucrose, which travels in solution to other parts of the plant (e.g., fruit, roots) or is used in the synthesis of the polysaccharides starch and cellulose

These Energy rich molecules were formed during the Light reactions of Photosynthesis.
This is the 5-Carbon molecule to which Carbon (CO2) is fixed.
This molecule can be used to form Glucose or to regenerate RuBP.
This reaction is called "Carbon Fixation".
This reaction requires Energy in the form of ATP.
These 2 molecules are formed from the breakdown of the product of Carbon Fixation.
During this reaction Carbon is reduced.

 

Some variations on Photosynthesis