The Calvin Cycle Basics
Dr. Melvin Calvin & Others
Dr. Calvin utilized carbon-14 isotopes as radioactive
tracers to reveal the chemical processes of
photosynthesis.
The Calvin Cycle
illustrates how
plants turn carbon
dioxide and water
into sugar.
The Calvin Cycle is a metabolic
pathway found in the stroma
of the chloroplast in which
inorganic carbon is fixed
into an organic form.
Dr. Calvin was also named “Mr. Photosynthesis” in
1961 by Time Magazine.
“…Dr. Calvin has long since earned the title: "Mr.
Photosynthesis." Shortly after World War II, he began to
use radioactive tracers, particularly carbon-14, and other
recently developed tools to find out what happens to
carbon dioxide when it tangles with chlorophyll in a living
green plant cell.
Step by painful step, Calvin and
his large group of helpers
followed CO2, tagged with
carbon-14, through the intricate
photosynthetic processes that start
when green leaves are exposed
to sunlight.”
Green algae (chlorella), grown in continuous cultures,
were placed in the "lollipop" with the light shining on
them. Carbon-14 labeled CO2 was injected into the
stream of nonradioactive CO2 for a suitable period, at
the end of which the algae were killed. The
compounds into which the radioactive carbon had
entered were analyzed by paper chromatography.
“But the greatest insight came to
Chemist Calvin one day while he
was in his car waiting at a traffic light.
After that, he and his group were
finally able to prove that sugar,
the finished product of the process,
is built up in six stages, each of
which adds a single carbon atom.
Now, thanks to Calvin, the chemical
action of chlorophyll, on which all life
on earth ultimately depends, is fairly
well understood…”
Time Nov. 10, 1961
Dr. Calvin & Dr. Benson were awarded the Nobel
Prize for Chemistry, in 1961, due to their
discovery of the cycle.
• The Calvin cycle fixes carbon dioxide and the adds
energy and hydrogen ions to the resulting molecules
to yield a three carbon phosphate sugar called
PGAL or G3P.
• The fixed (organic) carbon of PGAL is used to
produce the variety of organic compounds of living
organisms. It is used to keep the cycle going, and is
used to produce carbohydrates such as glucose.
Here’s What Happens…
This is called carboxylation.
Carbon is fixed here!
Rubisco
twelve 3-C PGALs
from #3
6) Two 3C PGALs form fructose & then
glucose.
• PGAL (G3P) and other sugar
phosphates from the Calvin cycle are
food for plants.
• PGAL molecules can be used to supply
energy and “carbon skeletons” for
metabolism in the plant.
Some sugar phosphates are made into
lipids, amino acids then protein. This
can occur in the chloroplast.
Humans and other animals consume
plants and thus use the material from
photosynthesis for building protein, as
well as a source of sugars and energy.
BSCS Biology