||The light independent process (also called
dark reactions or the Calvin-Benson cycle) takes place
in the stroma of the chloroplast. Carbon dioxide is modified
by series of chemical reactions to form carbohydrates.
The energy for these reactions comes from ATP and NADPH
generated during the light dependent process.
Carbon fixation, the incorporation of carbon dioxide into
an organic molecule, is the first step of the light independent
process. To form one molecule of glucose, 6 molecules of CO2
bind with Ribulose Bisphosphate (RuBP). This reaction is catalyzed
by the enzyme ribulose biosphosphate carboxylase/oxidase (RUBISCO).
Twelve molecules of 3-Phosphoglycerate (3PG) are the products
of this reaction.
from ATP and NADPH reduce the 3PG molecules to form another
3 carbon compound, glyceraldehyde-3-phosphate (G3P). Two G3P
molecules are removed from the cycle and ultimately become
one glucose molecule. The other 10 molecules of G3P are converted
back to RuBP molecules, ready to accept CO2 and
start the cycle again.