Photosynthesis

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The C3 pathway, also known as the Calvin Cycle, is a three-step process.  The reactants include water, carbon dioxide, a five-carbon molecule called RuBP, and an enzyme called RuBisCO that assembles the other reactants.  

 

The first step, called carboxylation, involved RuBisCO attaching a molecule of carbon dioxide to RuBP.  This results in a six-carbon molecule, whcih is too big.  

 

During the reduction phase, it splits into 2 3-carbon molecules, which are then reduced by ATP and NADPH.  One carbon is released during reduction, and is used to attach to other carbons that come out of more turns of the Calvin Cycle.

 

The last step of the Calvin Cycle is regeneration of RuBP.  ATP phosphorylates the now-reduced carbon chains, resulting in a five carbon chain that is ready for another turn of the cycle.  It requires six turns to form a single glucose molecule.

 

Despite the fact that 95% of all plants use this pathway, it commonly makes mistakes that are unhealthy for the plant.  This is called photorespiration.