A short review over Calvin Cycle.

1. CALVIN CYCLE
Introduction: -
A Quick review to the Photosynthesis,
ENERGY derived from the sun. Photosynthesis is the only process of biological
importance that can harvest this energy
using light.” More specifically, light energy drives the synthesis of carbohydrates from
carbon dioxide and water with the generation of oxygen
photosynthesis is:
Energy stored in these molecules can be used later to power; cellular processes in plants
and can serve as the energy source for all forms of life. A question might arise is
photosynthesis an endergonic reaction or exergonic reaction? The Answer is an ende
reaction because it requires an input of energy to occur; that energy comes in the form of
light.
The photosynthesis occurs in 2 stages:
1. The Light Reactions (or Light
2. The Calvin Cycle (or Calvin
Independent Reactions)
It cannot be overemphasized that energy is not made
the processes of photosynthesis and cellular respiration. That
thermodynamics. Photosynthesis is a process that
form” (light) into a “usable form” (organic compounds), and requires an intermediate step
(ATP/NADPH).
Photosynthesis follows the energy
Light Reaction
Light ATP/NADPH
Thylakoids
CALVIN CYCLE
A Quick review to the Photosynthesis, LIFE ON EARTH ULTIMATELY DEPENDS ON
ENERGY derived from the sun. Photosynthesis is the only process of biological
importance that can harvest this energy. The term photosynthesis means
More specifically, light energy drives the synthesis of carbohydrates from
carbon dioxide and water with the generation of oxygen. The net overall equation for
Energy stored in these molecules can be used later to power; cellular processes in plants
and can serve as the energy source for all forms of life. A question might arise is
reaction or exergonic reaction? The Answer is an ende
because it requires an input of energy to occur; that energy comes in the form of
The photosynthesis occurs in 2 stages: -
The Light Reactions (or Light-Dependent Reactions)
The Calvin Cycle (or Calvin-Benson Cycle or Dark Reactions
Independent Reactions)
phasized that energy is not made, but is instead transformed
the processes of photosynthesis and cellular respiration. That maintains the 1
thermodynamics. Photosynthesis is a process that converts energy from an “un
form” (light) into a “usable form” (organic compounds), and requires an intermediate step
s the energy,
Light
Calvin Cycle
ATP/NADPH Organic Compound
Stroma
1
LIFE ON EARTH ULTIMATELY DEPENDS ON
ENERGY derived from the sun. Photosynthesis is the only process of biological
The term photosynthesis means literally “synthesis
More specifically, light energy drives the synthesis of carbohydrates from
The net overall equation for
Energy stored in these molecules can be used later to power; cellular processes in plants
and can serve as the energy source for all forms of life. A question might arise is
reaction or exergonic reaction? The Answer is an endergonic
because it requires an input of energy to occur; that energy comes in the form of
Benson Cycle or Dark Reactions or Light-
transformed through
the 1st
law of
converts energy from an “un-usable
form” (light) into a “usable form” (organic compounds), and requires an intermediate step
Compound

2. The Calvin Cycle: -
The Calvin Cycle was explained by “Sir Melvin Calvin”
Second phase of the photosynthesis
Within which the chemical energy (from the light reactions
i.e. ATP/NADPH) and CO2 (from the atmosphere) are used to
produce organic compounds (like
occurs in the stroma of chloroplasts.
in the 3 steps:
1. Carbon Fixation,
2. Reduction, and
3. Regeneration of RUBP.
1. Carbon Fixation: -
This is the process of assimilating carbon from a non
and incorporating it into an organic compound (i.e. carbohydrates).
The proces is carried out in such a way that
carries 1 molecule of Cabondioxide
RUBP (a 5- carbon sugar) by RUBISCO, which is an enzyme also known as RUBP
Carboxylase. Simultaneously, other 5 stroma of the chloroplast might be running the
same procedure. So, a total Six Carbondioxide might be binding with 6 RUBP
molecule.
The Calvin Cycle was explained by “Sir Melvin Calvin”. The
Second phase of the photosynthesis i.e. The Calvin Cycle.
chemical energy (from the light reactions
(from the atmosphere) are used to
produce organic compounds (like glucose).The Calvin Cycle
of chloroplasts. The Calvin Cycle occurs
This is the process of assimilating carbon from a non-organic compound (i.e. CO
and incorporating it into an organic compound (i.e. carbohydrates).
proces is carried out in such a way that, consider only 1 Stroma of a chloroplast
carries 1 molecule of Cabondioxide from the atmosphere binds to the 1 molecule of
carbon sugar) by RUBISCO, which is an enzyme also known as RUBP
se. Simultaneously, other 5 stroma of the chloroplast might be running the
same procedure. So, a total Six Carbondioxide might be binding with 6 RUBP
2
organic compound (i.e. CO2)
and incorporating it into an organic compound (i.e. carbohydrates).
consider only 1 Stroma of a chloroplast
from the atmosphere binds to the 1 molecule of
carbon sugar) by RUBISCO, which is an enzyme also known as RUBP
se. Simultaneously, other 5 stroma of the chloroplast might be running the
same procedure. So, a total Six Carbondioxide might be binding with 6 RUBP

3. +
+
+
+
+
+
Here, it’s a point to note that one cycle binds one
stroma.
2. Reduction: -
Here, each of the 6- Carbon molecules within stroma
splints in half forming. Two 3
molecules produces Twelve 3
gaining electron from NADPH/ATP are a utilized for molecular rearranging.
Lets understand the process, As previously we have seen a total 6 Co2 binding with
6 RUBP further these Six 6
Twelve 3- Carbon molecules, which require NADPH and ATP as mentioned before.
6 Co2 6 RUBP Molecules
Here, it’s a point to note that one cycle binds one carbon dioxide with one RUBP within
Carbon molecules within stroma is very unstable which gets
splints in half forming. Two 3-Carbon molecule (i.e. a Total Six 6
molecules produces Twelve 3- Carbon molecule). Here the molecules get reduced by
gaining electron from NADPH/ATP are a utilized for molecular rearranging.
the process, As previously we have seen a total 6 Co2 binding with
6 RUBP further these Six 6- Carbon molecules beings unstable gets divided i
Carbon molecules, which require NADPH and ATP as mentioned before.
6 RUBP Molecules 6 Carbon (Unstable Structure)
3
with one RUBP within
very unstable which gets
Carbon molecule (i.e. a Total Six 6- Carbon
olecules get reduced by
gaining electron from NADPH/ATP are a utilized for molecular rearranging.
the process, As previously we have seen a total 6 Co2 binding with
Carbon molecules beings unstable gets divided into
Carbon molecules, which require NADPH and ATP as mentioned before.
6 Carbon (Unstable Structure)

4. 6 Carbons (Unstable Structure)
(Unstable Structure) G3P
4
G3P

5. A question might arise where did the NADPH and A
it is produced during the light reaction. Now, further as we know there are now
twelve 3- Carbon molecules which are known as G3P (
Phosphate) or PGAL (Phospho
with 30 carbons {i.e. 6 x 5
now 36- Carbons {i.e. 12 x 3
a net gain of 6- Carbons.
Here, A question might arise where did these 6
6 extra carbons came from the Co2
the atmosphere; these 6 additional carbons are denoted in red.
Out of which two of these “extra”
cycle. Thus, the Calvin Cycle “turns” 6 times, those 2 molecules of G3P combine to
form 1 molecule of glucose.
3PGAL
A question might arise where did the NADPH and ATP come from? The Answer is,
produced during the light reaction. Now, further as we know there are now
Carbon molecules which are known as G3P (Glyceraldehydes
Phosphate) or PGAL (Phospho-Glyceraldehyde). Since, we know the cycle started
i.e. 6 x 5- Carbon molecule (RUBP) = 30- Carbons} and there are
Carbons {i.e. 12 x 3- Carbon molecule (G3P) = 36- Carbons}. So, we have
Here, A question might arise where did these 6- Carbons come from? The Answer is
e from the Co2, which was obtained through the stomata from
the atmosphere; these 6 additional carbons are denoted in red.
Out of which two of these “extra” 3- Carbon G3P/PGAL molecules will exit the
cycle. Thus, the Calvin Cycle “turns” 6 times, those 2 molecules of G3P combine to
ucose.
3PGAL
1 Molecule Glucose
5
TP come from? The Answer is,
produced during the light reaction. Now, further as we know there are now
Glyceraldehydes 3,
. Since, we know the cycle started
Carbons} and there are
Carbons}. So, we have
Carbons come from? The Answer is
, which was obtained through the stomata from
/PGAL molecules will exit the
cycle. Thus, the Calvin Cycle “turns” 6 times, those 2 molecules of G3P combine to
1 Molecule Glucose

6. Here, the question may arise that 1 turn produces 6
made to glucose i.e. each turn can produce a molecule of glucose but, why is it
taking 6 turns to make 1 Glucose.
of mass that, the mass has to remain constant and that can be made if the RUBP is
regenerated and which requires 6 turns of Calvin Cycle.
3. Regeneration of RUBP: -
The remaining 10 G3P molecules (3
form 6 RUBP molecules (5
10 Molecules of G3P
Here, the question may arise that 1 turn produces 6- Carbons. So, then it can be
made to glucose i.e. each turn can produce a molecule of glucose but, why is it
taking 6 turns to make 1 Glucose. Because, as we remember the law of conservation
mass that, the mass has to remain constant and that can be made if the RUBP is
regenerated and which requires 6 turns of Calvin Cycle.
-
The remaining 10 G3P molecules (3-carbons each) get rearranged (using ATP) to
ules (5-carbons each).
10 Molecules of G3P 6 Molecules of
6
Carbons. So, then it can be
made to glucose i.e. each turn can produce a molecule of glucose but, why is it
Because, as we remember the law of conservation
mass that, the mass has to remain constant and that can be made if the RUBP is
carbons each) get rearranged (using ATP) to
Molecules of RUBP

7. The ATP utilized during this process came from the light reaction. So the end product
RUBP is regenerated again to run the cycle.
Summary to the Calvin Cycle: -
The ATP utilized during this process came from the light reaction. So the end product
again to run the cycle.
-
7
The ATP utilized during this process came from the light reaction. So the end product

8. In the Calvin Cycle, energy and electrons from the Light Reactions (in the form of ATP
and NADPH) and carbon dioxide from the atmosphere are used to produce organic
compounds. The Calvin Cycle occurs in the stroma inside the chloroplasts (inside the
cells). Carbon dioxide, ATP, and NADPH are required (reactants).
(G3P) are produced (products).
Summary to the Photosynthesis
A broad overview of photosynthesis,
sunlight and convert it to chemical energy in the form of ATP and NADPH through the use
of photo systems, electron transport chains, and chemiosmosis.
The Calvin Cycle (Phase 2) uses the ene
carbon dioxide to produce organic compounds.
In the Calvin Cycle, energy and electrons from the Light Reactions (in the form of ATP
and NADPH) and carbon dioxide from the atmosphere are used to produce organic
The Calvin Cycle occurs in the stroma inside the chloroplasts (inside the
Carbon dioxide, ATP, and NADPH are required (reactants). Organic compounds
(G3P) are produced (products).
Photosynthesis: -
tosynthesis, The Light Reactions (Phase 1) capture the energy in
sunlight and convert it to chemical energy in the form of ATP and NADPH through the use
, electron transport chains, and chemiosmosis.
The Calvin Cycle (Phase 2) uses the energy transformed by the light reactions along with
carbon dioxide to produce organic compounds. The photosynthetic equation is,
8
In the Calvin Cycle, energy and electrons from the Light Reactions (in the form of ATP
and NADPH) and carbon dioxide from the atmosphere are used to produce organic
The Calvin Cycle occurs in the stroma inside the chloroplasts (inside the
Organic compounds
The Light Reactions (Phase 1) capture the energy in
sunlight and convert it to chemical energy in the form of ATP and NADPH through the use
rgy transformed by the light reactions along with
The photosynthetic equation is,

9. Provides the
carbon to produce
organic
compounds during
the Calvin Cycle
Split during the
light reactions to
replace electrons
lost from
Photosystem II
Excites electrons during the
Light
Excites electrons during the
light reactions
The organic
compound ultimately
produced during the
Calvin Cycle
9
Produced as a
byproduct of the
splitting of water
during the light
reactions

10. 10
References: -
1. Principles of Biochemistry (6th
Edition), by Leninger ; Page No. 810-812.
2. Biology of Microorganisms (14th
Edition), by Brock; Page No. 390-392.
3. Plant Physiology (3rd
Edition), by Taiz & Zeiger; Page No. 146-150.