Calvin Cycle
LIGHT-INDEPENDENT REACTION
What is Calvin Cycle?
It is a process that takes place without the use light energy
or photons.
In Calvin Cycle, Carbon atoms from CO2 are fixed and used
to build three-carbon sugars. This process is fueled by, and
dependent on ATP and NADPH from the light reactions.
Unlike the light reactions, which takes place in the thylakoid
membrane, the reaction of Calvin Cycle take place in the
stroma
Reactants, Product and Enzymes
This process uses the by product of
light-dependent reaction (ATP and
NADPH) as an energy source and
Carbon Dioxide is also needed for the
series of chemical reactions. An enzyme
called RuBisCo (Ribulose-1,5bisphosphate carboxylase oxygenase),
catalyzes a reaction with CO2 and
another molecule RuBP (Ribulose
Biphosphate).
Stages of Calvin Cycle
The Calvin Cycle Reactions can be
divided into three main stages:
Carbon Fixation
Reduction
Regeneration
STAGE 1 (Carbon Fixation)
It is the stage where the CO2 is fixed from an inorganic
form into organic molecules. (CHEMOSYNTHESIS)
CO2, RuBisCO and 3 molecules of RuBP is present in the
Stroma
1 molecule of CO2 + 1 molecule of RuBP = two 3-carbon
compound (3-PGA)
PGA- phosphoglycerate
STAGE 2 ( Reduction)
After phosphate from ATP is added to 3-PGA, it resulted to
1, 3-biphosphoglycerate (1,3 BPGA)
Each 1,3 BPGA is reduced by 2 electrons of NADPH, this
results in the formation of PGAL (Phosphoglyceraldehyde) or
(G3P)
It is a type of Reduction Reaction because it gains electron
6 molecules of ATP and NADPH are used, converting it into
ADP and NADP+
After using ATP and NADPH, it retuned back to the thylakoid
where it can be reused and reenergized in light dependent
reaction
STAGE 3 (Regeneration)
6 molecules of PGAL or G3P is made, but only one is
sent out to the cytoplasm to contribute to formation of
other compounds needed by plants.
Since the G3P that is exported from the chloroplast has
3 carbon atoms, it takes 3 turns of the Calvin Cycle to fix
enough net of carbon to export one G3P. Each turn
makes two G3P, thus three tunes makes sic G3P.
One is exported while the remaining G3P molecules
remain in the cycle to regenerate the RuBP that will be
used in the carbon fixation.
3 molecules of ATP is used in the regeneration
Remember…
Safety First!
(Enter your own creative tag line above)