Photosynthesis 2: The Calvin Cycle
(Ch. 10)
1950s
|
1961
The Calvin
Cycle
Whoops! Wrong Calvin…
Remember what it means to be a plant…
• Need to produce all organic molecules necessary
for growth
– carbohydrates, lipids, proteins, nucleic acids
• Need to store chemical energy (ATP) produced
from light reactions
– in a more stable form
– that can be moved around plant
– saved for a rainy day
carbon + water + energy  glucose + oxygen
dioxide
6CO2 + 6H2O + light  C6H12O6 + 6O2
energy
Light reactions
• Convert solar energy to chemical energy
– ATP  energy
ATP
– NADPH  reducing power
• What can we do now?
  build stuff !!
photosynthesis
How is that helpful?
• Want to make C6H12O6
– synthesis
– How? From what?
What raw materials are available?
CO2
NADPH
carbon fixation
NADP
C6H12O6
reduces CO2
From CO2 => C6H12O6
• CO2 has very little chemical energy
– fully oxidized
• C6H12O6 contains a lot of chemical energy
– highly reduced
• Synthesis = endergonic process
– put in a lot of energy
• Reduction of CO2 => C6H12O6 proceeds in
many small uphill steps
– each catalyzed by a specific enzyme
– using energy stored in ATP & NADPH
From Light reactions to Calvin cycle
• Calvin cycle
– chloroplast stroma
• Need products of light reactions to drive
synthesis reactions
– ATP
– NADPH
ATP
thylakoid
stroma
Calvin cycle
C
C
C C C C C
1C
C C C C C
3. Regeneration
C C C C C
of RuBP
RuBP
starch,
sucrose,
cellulose
& more
ribulose bisphosphate
3 ATP
H H H
|
| |
C –C –C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
CO2
1. Carbon fixation
C C C C C C
RuBisCo
ribulose
bisphosphate
carboxylase
3 ADP
used
to make
glucose
C =C =C
5C
C
C C C C C C
6C
C C C C C C
5C
glyceraldehyde-3-P
G3P
C C C
PGA
phosphoglycerate
3C
6 NADP
C
C
C
C
C
C
6 ATP
2. Reduction
6 NADPH
3C
C
C
C
C
C
C
3C
6 ADP
C
C
C
C
C
C
H
|
H
|
H
|
Remember
G3P?
glycolysis
glucose
C-C-C-C-C-C
2 ATP
2 ADP
fructose-1,6bP
P-C-C-C-C-C-C-P
DHAP
P-C-C-C
G3P
glyceraldehyde
3-phosphate
C-C-C-P
2 NAD+
2
4 ADP
Photosynthesis
pyruvate
C-C-C
4 ATP
To G3P and Beyond!
To G3P
and beyond!
• Glyceraldehyde-3-P
– end product of Calvin cycle
– energy rich 3 carbon sugar
– “C3 photosynthesis”
• G3P is an important intermediate
• G3P => glucose => carbohydrates
=>
=>
=>
lipids => phospholipids, fats, waxes
amino acids => proteins
nucleic acids => DNA, RNA
RuBisCo
• Enzyme which fixes carbon from air
– ribulose bisphosphate carboxylase
– the most important enzyme in the world!
• it makes life out of air!
– definitely the most abundant enzyme
I’m green
with envy!
AP Biology
It’s not easy
being green!
Accounting
• The accounting is complicated
– 3 turns of Calvin cycle = 1 G3P
– 3 CO2 => 1 G3P (3C)
– 6 turns of Calvin cycle = 1 C6H12O6 (6C)
– 6 CO2 => 1 C6H12O6 (6C)
– 18 ATP + 12 NADPH => 1 C6H12O6
– any ATP left over from light reactions will be
used elsewhere by the cell
Photosynthesis summary
• Light reactions
– produced ATP
– produced NADPH
– consumed H2O
– produced O2 as byproduct
• Calvin cycle
– consumed CO2
– produced G3P (sugar)
– regenerated ADP
– regenerated NADP
Light Reactions
light => ATP + NADPH + O
2
energy
H2O +
H2O
sunlight
Energy Building
Reactions
NADPH
ATP
O2
 produces ATP
 produces NADPH
 releases O2 as a
waste product
Calvin Cycle
CO2 + ATP + NADPH => C6H12O6 + ADP + NADP
CO2
ADP
NADP
Sugar
Building
Reactions
NADPH
ATP
sugars
 builds sugars
 uses ATP &
NADPH
 recycles ADP
& NADP
 back to make more
ATP & NADPH
Putting it all together
light
CO2 + H2O + energy => C6H12O6 + O2
H2O
CO2
sunlight
ADP
Energy NADP
Building
Reactions
Sugar
Building
Reactions
NADPH
ATP
O2
sugars
Plants make both:
energy
ATP & NADPH
sugars
even though
this equation
is a bit of a lie…
it makes a
better story
Energy cycle
sun
Photosynthesis
light
CO2 + H2O + energy => C6H12O6 + O2
plants
CO2
glucose
H2O
animals, plants
ATP
C6H12O6 + O2 => energy + CO2 + H2O
Cellular Respiration
The Great Circle
of Life,Mufasa!
ATP
O2
Summary of photosynthesis
6CO2 + 6H2O + light => C6H12O6 + 6O2
energy
•
•
•
•
•
•
•
•
•
•
Where did the CO2 come from?
Where did the CO2 go?
Where did the H2O come from?
Where did the H2O go?
Where did the energy come from?
What’s the energy used for?
What will the C6H12O6 be used for?
Where did the O2 come from?
Where will the O2 go?
What else is involved…not listed in this equation?
Supporting a biosphere
• On global scale,
photosynthesis is the
most important process
for the continuation of life on Earth
– each year photosynthesis…
• captures 121 billion tons of CO2
• synthesizes 160 billion tons of carbohydrate
– heterotrophs are dependent on plants as food
source for fuel & raw materials
If plants can do it…
You can learn it!
Ask Questions!!
Review Questions
1. The final product of the Calvin Cycle is
A.
B.
C.
D.
E.
Carbon dioxide
Fructose
Glucose
G3P
Oxygen
2. Which of the following is true of the Calvin
Cycle
A. It is controlled by enzymes in the stroma
B. It takes place in the thylakoid disks of the inner
chloroplast membrane
C. Carbon dioxide is a product
D. It is an ATP-independent process
E. One cycle consumes four molecules of PGAL
3. If a toxin was administered to a plant that
prevented the action of ribulose
bisphosphate carboxylase, which of the
following steps of the Calvin cycle would be
most directly affected?
A. Regeneration of RUBP
B. Donation of phosphates from ATP to Calvin cycle
intermediary compounds
C. The initial fixation of carbon dioxide
D. Oxidation of NADPH
E. Production of Glucose.