The Calvin Cycle Basics
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.
• 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!
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.