PHOTOSYNTHESIS
Calvin Cycle:
Life from Air
Whoops! Wrong
Calvin…
THE
CALVIN
CYCLE
REMEMBER WHAT IT
MEANS TO BE A PLANT
• Need to produce all organic molecules
necessary for life
• 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 the plant
• Than can be saved for a rainy day
carbon + water + energy  glucose + oxygen
dioxide
C6H12O6
6CO2 + 6H2O +light
+ 6O2

energy
LIGHT REACTIONS
• Convert solar energy to chemical energy
• ATP  energy
• NADPH  reducing power
• What now?
• Build stuff!!
photosynthesis
ATP
HOW IS THAT HELPFUL?
• Want to make C6H12O6
• How? From what?
• What raw materials are available??
ATP
CO2
FROM CO2  C6H12O6
• CO2 has very little chemical
energy
• Fully oxidized
CO2
• C6H12O6 contains a lot of
chemical energy
NADPH
• Highly reduced
NADP
• Synthesis = endergonic process
• Put in a lot of energy
• Reduction of CO2  C6H12O6
proceeds in many small uphill
steps
C6H12O6
• Each catalyzed by a specific enzyme
• Uses the energy stored in ATP &
NADPH
carbon fixation
• Calvin cycle
FROM LIGHT REACTIONS
TO CALVIN CYCLE
• Occurs in the stroma
• Need products of light reactions to drive
synthesis reactions
• ATP
• NADPH
ATP
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
|
CALVIN CYCLE
G3P
• We’ve seen
G3P before?
• Do you
remember
where?
glucose
C-C-C-C-C-C
2
2
ATP
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
glycolysis
Photosynthesis
pyruvate
C-C-C
2
2
NAD+
4
ADP
4
ATP
TO G3P & BEYOND
• Glyceraldehyde-3-P
• End product of Calvin cycle
• Energy rich 3-carbon sugar
• “C3 photosynthesis”
• G3P is an important intermediate
G3P  glucose  carbohydrates
G3P  lipids  phospholipids, fats, waxes
G3P  amino acids  proteins
G3P  nucleic acids  DNA, RNA
RUBISCO
• Enzyme responsible for carbon fixation
• Ribulose bisphosphate carboxylase
• RuBisCo
• The most important enzyme in the world!
• It makes life out of AIR!
• Definitely the most abundant enzyme
I’m green
with envy!
It’s not easy
being green!
ACCOUNTING
• The accounting is complicated
• 3 turns of Calvin cycle = 6G3P
• 3 CO2 = 6G3P
• 6 turns of Calvin cycle = 1 C6H12O6
• 6 CO2 = 1 C6H12O6
• 18 ATP + 12 NADPH  1 C6H12O6
• Any leftover ATP from light reactions will be
used elsewhere by the cell
• Growth, reproduction, movement, etc
ACCOUNTING
• The accounting is complicated
• Now we need to generate RuBP
• 5 G3P = 3 RuBP
• 3 CO2  6 G3P  3 RuBP + ½ C6H12O6
PHOTOSYNTHESIS SUMMARY
• Light reactions
•
•
•
•
Produced ATP
Produced NADPH
Consumed H2O
Produced O2 as a
byproduct
• Calvin cycle
•
•
•
•
Consumed CO2
Produced G3P (sugar)
Regenerated ADP
Regenerated NADP
ADP
NADP
LIGHT REACTIONS
ATP + NADPH + O2
H2O + light

energy
H2O
•
•
•
•
sunlight
Energy Building
Reactions
NADPH
ATP
O2
Produced ATP
Produced NADPH
Consumed H2O
Produced O2 as a
byproduct
CALVIN CYCLE
CO2 + ATP + NADPH  C6H12O6 + ADP + NADP
CO2
ADP
NADP
Sugar
Building
Reactions
NADPH
ATP
sugars
•
•
•
•
Consumed CO2
Produced sugar
Used ATP & NADPH
Regenerated ADP
&NADP
PUTTING IT ALL TOGETHER
light
CO2 + H2O + energy  C6H12O6 + O2
H2O
CO2
sunlight
• Plants make
energy
• ATP & NADPH
ADP
Energy NADP
Building
Reactions
Sugar
Building
Reactions
NADPH
ATP
O2
sugars
• Plants store energy
as sugar
sun
even though
this equation
is a bit of a lie…
it makes a
better story
ENERGY CYCLE
Photosynthesis
light
CO2 + H2O + energy  C6H12O6 + O2
plants
CO2
H2O
glucose
animals, plants
ATP
C6H12O6 + O2  energy + CO2 + H2O
Cellular Respiration
The Great Circle
of Life!
ATP
O2
PHOTOSYNTHESIS SUMMARY
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 did the O2 go?
• What is missing from this equation?
SUPPORTING THE BIOSPHERE
• On a 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
carbohydrates
• Heterotrophs are dependent
on plants as a food source
for fuel & raw materials
If plants can
do it, then you
can learn it.
Any questions?