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10/10/2012
Life’s Energy Needs
• All life needs a constant input of energy
– Heterotrophs (Animals)
• get their energy from “eating others”
– eat food = other organisms = organic molecules
• make energy through respiration
– Autotrophs (Plants)
•
•
•
•
produce their own energy (from “self”)
convert energy of sunlight
build organic molecules (CHO) from CO2
make energy & synthesize sugars through
photosynthesis
Energy Connections
• Heterotrophs
– Making energy and organic molecules from ingesting
organic molecules
glucose + oxygen  carbon + water + energy
dioxide
C6H12O6 + 6O2  6CO2 + 6H2O + ATP
OXIDATION = EXERGONIC
• Autotrophs
– Making energy and organic molecules from light energy
carbon + water + energy  glucose + oxygen
dioxide
6CO2 + 6H2O + ATP  C6H12O6 + 6O2
REDUCTION = ENDERGONIC
Plant Needs
• Need to…
– collect light energy
ATP
• transform it into chemical energy
– store light energy
glucose
• in a stable form to be
moved around the plant or stored
– need to get building block atoms
from the environment
CO2
• C, H, O, N, P, K, S, Mg
– produce all organic molecules
needed for growth
H2 O
N
K P
…
• carbohydrates, proteins, lipids, nucleic acids
Plant Structure
• Obtaining raw materials
– sunlight
• leaves = solar collectors
– CO2
• stomates = gas exchange
– H2O
• uptake from roots
stomata
– nutrients
• N, P, K, S, Mg, Fe…
• uptake from roots
transpiration
gas exchange
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10/10/2012
Chloroplasts
cross section
of leaf
leaves
Plant Structure
• Chloroplasts
absorb
sunlight & CO2
CO2
• fluid-filled interior
outer membrane
inner membrane
stroma
• Thylakoid membrane contains
chloroplasts
contain
chlorophyll
make
energy & sugar
Light Reactions
• Light reactions
• Electron Transport Chain
– light-dependent reactions
– energy conversion reactions
• convert solar energy to chemical
energy
• ATP & NADPH
• Calvin cycle
– light-independent reactions
– sugar building reactions
• uses chemical energy (ATP & NADPH)
to reduce CO2 & synthesize C6H12O6
ETC of Respiration
• Mitochondria transfer chemical energy from food
molecules into chemical energy of ATP
use electron carrier NADH
thylakoid
granum
• H+ gradient built up within
thylakoid sac
Photosynthesis

+
– double membrane
– stroma
– chlorophyll molecules
– electron transport chain
– ATP synthase
chloroplast
+
H
+H
+
H+ H+ H + H+ H+ HH+
H+ Hthylakoid
ATP
– thylakoid sacs
– grana stacks
chloroplasts
in plant cell
chloroplast
thylakoid
chloroplast
ATP
+ H+ H+ H+
H+ H+ H
+ + + +
H+ H H H H
+ H+ H+ H+
H+ H+ H
+ H+ H+ H+
+
H
H
• There is also one on Cellular Respiration
– proteins in organelle membrane
– electron acceptors
• NADPH
– proton (H+)
gradient across
inner membrane
• find the double membrane!
– ATP synthase
enzyme
ETC of Photosynthesis
• Chloroplasts transform light energy into
chemical energy of ATP
 use electron carrier NADPH
generates O2
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10/10/2012
ATP Synthase
• Enzyme that
• moves the electrons
• runs the pump
• pumps the protons
PHOTOSYNTHESIS
(sunlight)
CELLULAR RESPIRATION
(breakdown of C6H12O6)
• builds the gradient
H+
H+
• drives the flow of protons
H+
H+
H+
H+
H+
H+
through ATP synthase
• bonds Pi to ADP
• generates the ATP
ADP + Pi
ATP
H+
Electromagnetic Spectrum
Photosynthesis Pigments
Light
• Photosynthesis gets energy by absorbing wavelengths of
light
– chlorophyll a
• absorbs best in red & blue wavelengths & least in green
– accessory pigments with different structures absorb
light of different wavelengths
• chlorophyll b, carotenoids, xanthophylls
• Chlorophylls & other pigments
– embedded in thylakoid
membrane
– arranged in a “photosystem”
• collection of molecules
– structure-function relationship
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10/10/2012
Photosystems of Photosynthesis
ETC of Photosynthesis
chlorophyll a
• 2 photosystems in thylakoid membrane
Photosystem II
chlorophyll b
– collections of chlorophyll molecules
– act as light-gathering molecules
– Photosystem II
• chlorophyll a
• P680 = absorbs 680nm
wavelength red light
Photosystem I
reaction
center
– Photosystem I
• chlorophyll b
• P700 = absorbs 700nm
wavelength red light
antenna
pigments
ETC of Photosynthesis
ETC of Photosynthesis
thylakoid
chloroplast
ATP
O2
sun
+ H+ H+ H+
H+ H+ H
+ + + +
H+ H H H H
+ H+ H+ H+
H+ H+ H
+ + + +
H+ H H H H
Plants SPLIT water!
1
e
e
O
O
H
e
e
+H
e-
H
2
e
e
O
H H
1
e-
H+
fill the e– vacancy
Photosystem II
P680
chlorophyll a
Photosystem II
P680
chlorophyll a
ETC of Photosynthesis
ETC of Photosynthesis
thylakoid
chloroplast
+ H+ H+ H+
H+ H+ H
+ + + +
H+ H H H H
+ H+ H+ H+
H+ H+ H
+ + + +
H+ H H H H
ATP
3
2
e
e
1
e
e
H+
sun
5
4
ATP
H+
H+
H+
Photosystem II
P680
chlorophyll a
H+
to Calvin Cycle
e
H+
H+
+
H+ H
H+
energy to build
carbohydrates
Photosystem II
P680
chlorophyll a
ADP + Pi
ATP
e
Photosystem I
P700
chlorophyll b
H+
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10/10/2012
ETC of Photosynthesis
ETC of Photosynthesis
electron carrier
6
e
e
sun
sun
+
5
O
sun
+
H
+
H+ H H+ H+ H +
H
H+
H+ H+ H+
to Calvin Cycle
split H2O
Photosystem II
P680
chlorophyll a
Photosystem I
P700
chlorophyll b
ATP
$$ in the bank…
reducing power!
ETC of Photosynthesis
Phosophorylation
• ETC uses light energy to produce
– ATP & NADPH
• go to Calvin cycle
• PS II absorbs light
– excited electron passes from chlorophyll to “primary electron
acceptor”
– need to replace electron in chlorophyll
– enzyme extracts electrons from H2O & supplies them to
chlorophyll
• splits H2O
• O combines with another O to form O2
• O2 released to atmosphere
• and we breathe easier!
Phosophorylation
cyclic
photophosphorylation
NADP
NON cyclic
photophosphorylation
ATP
Non-cyclic Phosphorylation
• Light reactions elevate electrons in
2 steps (PS II & PS I)
– PS II generates
energy as ATP
– PS I generates
reducing power as NADPH
ATP
ATP
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10/10/2012
Cyclic Phosphorylation
Photosynthesis (ETC) Summary
• If PS I can’t pass electron
to NADP…it cycles back
to PS II & makes more
ATP, but no NADPH
6CO2 + 6H2O + light energy  C6H12O6 + 6O2

– coordinates light reactions
to Calvin cycle
– Calvin cycle uses more ATP
than NADPH
ATP
18 ATP +
12 NADPH
 1 C6H12O6
There’s more to Photosynthesis
than the ETC…
IT’s CALVIN CYCLE
TIME!!!
Light Reactions
• Convert solar energy to chemical energy
– ATP
– NADPH
ATP
•
•
•
•
•
•
•
•
•
•
Where did the energy come from?
Where did the electrons come from?
Where did the H2O come from?
Where did the O2 come from?
Where did the O2 go?
Where did the H+ come from?
Where did the ATP come from?
What will the ATP be used for?
Where did the NADPH come from?
What will the NADPH be used for?
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
photosynthesis
• Want to make C6H12O6
– synthesis
– How? From what?
What raw materials are available?
• What can we do now?
CO2
NADPH
carbon fixation
reduces CO2
NADP
C6H12O6
NADP
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10/10/2012
From Light reactions to
Calvin cycle
From CO2  C6H12O6
• CO2 has very little chemical energy
• Calvin cycle
– fully oxidized
– chloroplast stroma
• C6H12O6 contains a lot of chemical energy
• Need products of light reactions to drive synthesis
reactions
stroma
– highly reduced
• Synthesis = endergonic process
– put in a lot of energy
– ATP
– NADPH
• Reduction of CO2  C6H12O6 proceeds in many
small uphill steps
ATP
– each catalyzed by a specific enzyme
– using energy stored in ATP & NADPH
thylakoid
Calvin cycle
C
C
1C
C C C C C
3. Regeneration
of RuBP
C C C C C
C C C C C
RuBP
ribulose bisphosphate
starch,
sucrose,
cellulose
& more
C= C= C
H H H
| | |
C– C– C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
RuBisCo
ribulose
bisphosphate
carboxylase
3 ADP
used
to make
glucose
CO2
1. Carbon fixation
C C C C C C
6C
C C C C C C
5C
glyceraldehyde-3-P
G3P
glucose
C-C-C-C-C-C
(will come in to play with
Cellular Respiration)
2
2
C C C C C C
5C
3 ATP
G3P
C
C C C
PGA
phosphoglycerate
C
C
C
C
C
C
3C
3C
6 NADP
glycolysis
P-C-C-C-C-C-C-P
DHAP
C
C
C
C
C
C
3C
P-C-C-C
6 ADP
H
|
H
|
H
|
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
ADP
fructose-1,6bP
G3P
glyceraldehyde
3-phosphate
C-C-C-P
6 ATP
2. Reduction
6 NADPH
C
C
C
C
C
C
ATP
Photosynthesis
pyruvate
2
2
NAD+
4
ADP
4
ATP
C-C-C
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
  lipids   phospholipids, fats, waxes
  amino acids   proteins
  nucleic acids   DNA, RNA
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10/10/2012
Calvin Cycle Accounting
Photosynthesis summary
• Light reactions
• 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)
– produced ATP
– produced NADPH
– consumed H2O
– produced O2 as byproduct
• Calvin cycle
– 18 ATP + 12 NADPH  1 C6H12O6
– any ATP left over from light reactions will be used
elsewhere by the cell
Light Reactions
– consumed CO2
– produced G3P (sugar)
– regenerated ADP
– regenerated NADP
H2O
CO2 + ATP + NADPH  C6H12O6 + ADP + NADP
 produces ATP
 produces NADPH
 releases O2 as a
waste product
Energy Building
Reactions
 builds sugars
 uses ATP &
NADPH
 recycles ADP &
NADP
CO2
ADP
NADP
Sugar
Building
Reactions
NADPH
NADPH
ATP
ATP
 back to make more
ATP & NADPH
sugars
O2
Putting it all together
CO2
NADP
Calvin Cycle
H2O + light
 ATP + NADPH + O2
energy
sunlight
ADP
light
+ H2O + energy  C6H12O6 + O2
H2O
CO2
sunlight
ADP
Energy
Building
Reactions
NADP
Sugar
Building
Reactions
NADPH
Plants make both:
 energy
 ATP & NADPH
 sugars
Energy
Cycle
sun
Photosynthesis
light
CO2 + H2O + energy  C6H12O6 + O2
PLANTS
CO2
glucose
H2 O
ANIMAL AND PLANTS
C6H12O6
O2
ATP
+ O2  energy + CO2 + H2O
Cellular Respiration
ATP
ATP
O2
sugars
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10/10/2012
Photosynthesis (CC) Summary
Photorespiration
6CO2 + 6H2O + light energy  C6H12O6 + 6O2
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?
• In most plants (C3 plants), initial fixation of CO2, via
rubisco, forms a three-carbon compound
• In photorespiration, rubisco adds O2 instead of CO2 in the
Calvin cycle
•
•
•
•
•
•
•
•
•
•
– Photorespiration consumes O2 and organic fuel and releases
CO2 without producing ATP or sugar
– Photorespiration may be an evolutionary relic because rubisco
first evolved at a time when the atmosphere had far less O2 and
more CO2
– Photorespiration limits damaging products of light reactions
that build up in the absence of the Calvin cycle
– In many plants, photorespiration is a problem because on a hot,
dry day it can drain as much as 50% of the carbon fixed by the
Calvin cycle
C4 Plants
• C4 plants minimize the cost of photorespiration by
incorporating CO2 into four-carbon compounds in
mesophyll cells
• This step requires the enzyme PEP carboxylase
• PEP carboxylase has a higher affinity for CO2 than rubisco
does; it can fix CO2 even when CO2 concentrations are
low
• These four-carbon compounds are exported to bundlesheath cells, where they release CO2 that is then used in
the Calvin cycle
CAM Plants
• Some plants, including succulents (cacti), use
crassulacean acid metabolism (CAM) to fix carbon
• CAM plants open their stomata at night,
incorporating CO2 into organic acids
• Stomata close during the day, and CO2 is released
from organic acids and used in the Calvin cycle
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10/10/2012
Factors Affecting Photosynthesis
•
•
•
•
•
Light Quality
Light Intensity
Light Period
CO2 Availability
H2O Availability
The importance of
Photosynthesis
• The energy entering chloroplasts as sunlight gets
stored as chemical energy in organic compounds
• Sugar made in the chloroplasts supplies chemical
energy and carbon skeletons to synthesize the
organic molecules of cells
• Plants store excess sugar as starch in structures
such as roots, tubers, seeds, and fruits
• In addition to food production, photosynthesis
produces the O2 in our atmosphere
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
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