The Calvin Cycle Process


The BIG Picture!

 Before continuing, be sure to familiarize yourself with the 

important players in the Calvin Cycle by going here.

Phase 1: Carbon Fixation

 

CO2 comes into the stroma of the chloroplast via the stomata of the leaves.  Rubisco catalyzes the bonding of CO2 to RuBP to create an unstable 6-carbon molecule that instantly splits into two 3-carbon molecules of 3-PG.

 

 

 

   

 

Phase 2: Reduction

 

ATP phosphorylates each 3-PG molecule and creates 1,3-bisphosphoglycerate.  This in turn results in the loss of the terminal phosphate group from ATP (adenosine triphosphate) thus making ADP (adenosine diphosphate).

 

 

 

 

 

These pictures show the difference between ATP and ADP.  ATP (left) has a tail of three phosphate groups.  The molecule then donates the terminal phosphate group and becomes ADP with only two phosphate groups.

 

 

 

 

 

 

 

    

NADPH reduces 1,3-bisphosphoglycerate which causes the phosphate group to break off once again.  The molecule then picks up a proton (H+) from the medium to become glyceraldehyde-3-phosphate.  The broken off phosphate group also gains a proton to become H3PO4.  NADPH is oxidized by this process and becomes NADP+.

 

These pictures show the difference between NADPH (left) and NAP+ (right).  In NAP+, the nitrogen has 4 bonds giving the molecule an overall positive charge.

 

 

 

 

Below are the three intermediates of the reduction phase of the Calvin cycle.  Note the only difference between each molecule is the group attached to the primary carbon (the lowest carbon -- with the carbonyl.)

Phase 3: Regeneration

For every six molecules of G3P created five molecules continue on to phase 3 while one leaves to be used for organic compounds. 

 

 

 

 

ATP is once again needed.  However, this time it phosphorylates G3P to regenerate RuBP after some rearrangement.

 

 

 

 

 

 

Output of Calvin Cycle:

G3P is combined to form fructose.

 

 

 

 

 

 

 

Fructose is then rearranged to create glucose.

 

 

 

 

 

 

 

 

Fructose and glucose then undergo dehydration and form a glycosidic linkage to create the disaccharide sucrose and water.  Sucrose is then transported throughout the plant.

 

 

 

 

 

 

This page was created by: Sze-Ling Ng and EmmaLeigh Smith

Last Updated: February 25, 2002

For more information or comments, contact ngszelin@msu.edu or smithe44@msu.edu