The Calvin cycle is a process used by autotrophs like plants and algae to convert carbon dioxide from the air into glucose. It involves three main phases: carbon fixation, reduction, and regeneration of the starting molecule RuBP. In carbon fixation, the enzyme rubisco attaches CO2 to RuBP. The resulting unstable 6-carbon molecule splits into two 3-carbon phosphoglycerate molecules. In reduction, ATP and NADPH add phosphate and hydrogen to convert phosphoglycerate into glyceraldehyde-3-phosphate (G3P). Five of the six G3Ps are recycled to regenerate three RuBP molecules. The remaining G3P can be converted into glucose or other carbohydrates.

1. ENERGY
TRANSFORMATION
(CALVIN CYCLE)

2. Calvin Cycle
•On Earth, every living thing is a carbon-based
life form. This just implies that the intricate
molecules that make up your incredible body
are supported by carbon backbones.
•The Calvin cycle or “dark reactions” is a
process that autotrophs, like plants and
algae, use to make carbon dioxide from the
air into Glucose (C6H12O6) which is a sugar,
the food they need to grow.

3. There are three main stages in a Calvin
Cycle: Carbon fixation, Reduction, and
Regeneration of the starting molecule.
Phase 1: Carbon Fixation
Phase 2: Reduction
Phase 3: Regeneration of
RuBP

4. • Carbon fixation is a process of merging
CO2, an inorganic carbon molecule into an
organic material.
• In this phase, the CO2 molecule is
attached to a five-carbon sugar molecule,
ribulose biphosphate (RuBP) with the help
an enzyme named rubisco or RuBP
carboxylase, believed to be the most
abundant protein in the chloroplast and
probably on Earth.
Phase 1: Carbon Fixation

5. • The resulting product of carbon fixation is
a six-carbon sugar, which is extremely
unstable and immediately splits in half.
The split forms two molecules of a 3-
phosphoglycerate(3-Carbon).

7. • In reduction phase, a phosphate group
(from ATP) is then attached to each 3-
phosphoglycerate by an enzyme, forming
1,3-phosphoglycerate.
• To produce Glyceraldyde-3-phosphate G3P,
NADPH swoops in and reduces 1,3
biphosphogycerate.
• The produced six G3Ps by the Calvin Cycle,
five are recycled to give three molecules of
RuBP.
Phase 2: Reduction

8. • Of the six G3P’s produced, only one G3P
leaves the cycle to be packaged for use by
the cell. It needs two molecules of G3P to
make one molecule of glucose.
• The products formed during the Calvin cycle,
ADP and NADP+, will then be brought back to
the thylakoid membrane and then will enter
the light reactions. Inside the thylakoid, they
will be ‘recharged’ with energy and become
ATP and NADPH.

10. Phase 3: Regeneration of RuBP
• Five molecules of Glyceraldyde-3-
phosphate G3P shall undergo complex
enzymatic reactions to produce three
molecules of Ribulose Biphosphate
(RuBP).
• The cell needs another three molecules
of ATP, but also provides another set of
Ribulose Biphosphate (RuBP) to continue
the cycle.

12. G3P after its release from the cycle
• The two Glyceraldyde-3-phosphate G3Ps can
combine to form six-carbon sugar. They could
either be glucose or fructose (C6H12O6).
• Eventually, glucose and fructose can be combined
to form sucrose. Starch is formed when glucose is
connected in chains. In lipid and protein synthesis
G3Ps can also be used.

14. Making of a Carbohydrate
In making one molecule of G3P, the chloroplast
needs the following:
1. 3 molecules of CO2
2. 9 molecules of ATP
3. 6 molecules of NADPH

15. Important points to know in the
Calvin Cycle
• The sugar produced in the Calvin Cycle is not the
six-carbon Glucose that we are familiar with. The
product in the Calvin Cycle is a three-carbon
sugar known as G3P or Glyceraldehyde-3-
Phosphate.The glucose is formed later on.
• There is a need for the Calvin Cycle to ‘spin’ three
times to make one molecule of Glyceraldehyde-3-
Phosphate (G3P) from three molecules of CO2.