3.3 photosynthesis… the details photosynthesis is divided into 2 sequential processes 1.light...
TRANSCRIPT
3.3 Photosynthesis…The Details
• Photosynthesis is divided into 2 sequential processes
1. Light reaction (stages 1 and 2)
2. Carbon Fixation (Calvin Cycle) (stage 3)
Overview of Photosynthesis
6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O
• Photosynthesis, like cellular respiration, is a series of redox reactions!
6 CO2 12 H2OReactants
Products C6H12O6 6H2O 6O2
Tracking Atoms in Photosynthesis…
What does this suggest about photosynthesis?
6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O
The sugars that result from photosynthesis are
produced by adding the hydrogen ions and electrons
from water to carbon dioxide, NOT by splitting CO2 and
adding water!oxidized
reduced
H+ and e-
The stages of photosynthesis…
Light Dependent Reactions
• Occurs along the thylakoid membrane
• this is where H2O is oxidized.
• chemiosmotic production of ATP!
• electron carrier (NADPH) is synthesized
Light Reaction
• Divided into 3 parts;
1. Photoexcitation-absorption of a photon by an electron of chlorophyll
2. Photosystems and the ETC
3. Chemiosmosis (sound familiar?)
Photoexcitation
• Before photons strike chlorophyll, their electrons are at ground state (lowest potential energy)
• Once the photon strikes the electron it becomes “excited” and moves to a higher potential energy level
• The electron eventually goes back to ground state (loss of potential energy appears as heat and light-fluorescence if it is not used in photosynthesis)
Photoexcitation
• Most chlorophyll do not fluoresce while in a thylakoid memebrane b/c the excited electron is captured by the primary electron acceptor
• This is a redox rxn-the chlorphyll is oxidized and the primary acceptor is reduced
Photosystems and the ETC
ETC of Photosynthesis
Chloroplasts transform light energy into chemical energy of ATP
use electron carrier NADPH
generates O2
PETCPhoton
Photosystem
Photosynthetic Electron Transfer Chain (PETC)
• series of electron carriers which take electrons from photosystem, and..
• ultimately carry electrons to NADP+
Photosystems
• Experiments in the 1940’s suggested that light photons are
absorbed at 2 different points along the same PETC.…
• In fact, there are two Photosystems in operation
ETC of Photosynthesis
Photosystem II
Photosystem I
chlorophyll a
chlorophyll b
1
ETC of Photosynthesis
ee
sun
Photosystem IIP680
chlorophyll a
12
ETC of Photosynthesis
Photosystem IIP680
chlorophyll a
OH H
H
H
Inhale, baby!
e e
ee
e-
e-
H+H+
H+H+
H+H+
H+H+
H+H+
H+
H+H+
H+H+
H+H+
H+H+
H+H+
H+ATP
thylakoidchloroplast
H+
+H
OO
SPLIT water!
fill the e– vacancy
12
H+
H+
3
4
H+
ADP + Pi
H+H+
H+
H+ H+
H+H+H+
ee
e e
ATP
to Calvin Cycle
energy to buildcarbohydrates
H+H+
H+H+
H+H+
H+H+
H+H+
H+
H+H+
H+H+
H+H+
H+H+
H+H+
H+ATP
thylakoidchloroplast
Photosystem IIP680
chlorophyll a
ETC of Photosynthesis
ATP
ee
e e
sun
5
Photosystem IIP680
chlorophyll a
Photosystem IP700
chlorophyll b
e e
ETC of Photosynthesis
e e fill th
e e– vacancy
6
electron carrier
ee
e e
5sun
NADPH toCalvin Cycle
Photosystem IIP680
chlorophyll a
Photosystem IP700
chlorophyll b$$ in the bank…reducing power!
ETC of Photosynthesis
split H2O
ETC of Photosynthesis
O
ATP
to Calvin CycleH+
H+
H+
H+
H+
H+
H+
H+
H+H+
H+
e e
e e
sun sun
Terms• Primary electron acceptor-pheophytin (PSII)• PQ-Plastoquinone (PSII)• Z protein-splits water (PSII) the 2 electrons are used to replace
the ones lost in P680, oxygen leaves as “waste” and the protons remain adding to the gradient
• B6-f cytochrome complex (PSII)• Pc-Plastocyanin (PSII)• Fd-ferredoxin (PSI)• NADP reductase (PSI) uses 2 electrons and H+ to reduce
NADP+ to NADPH (b/c 2 electrons are needed this process must occur twice)
• ATP is created by chemiosmosis due to the proton gradient in the thylakoid lumen-this drives ATP synthase. 4 protons are move into the lumen for each pair of electrons that move through the ETC
ETC of Photosynthesis• ETC uses light energy to produce
– ATP & NADPH (called noncyclic electron flow)• go to Calvin cycle
• PS II absorbs light– excited electron passes from chlorophyll to
“primary electron acceptor-pheophytin”– need to replace electron in chlorophyll– Enzyme (z protein) extracts electrons from H2O &
supplies them to chlorophyll• splits H2O (h protons)• O combines with another O to form O2
• O2 released to atmosphere• and we breathe easier!
Noncyclic Photophosphorylation
• 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
Cyclic photophosphorylation• If PS I can’t pass electron
to NADP…it cycles back to PS II & makes more ATP, but no NADPH– coordinates light reactions
to Calvin cycle– Calvin cycle uses more
ATP than NADPH
18 ATP +12 NADPH
1 C6H12O6
ATP
Photophosphorylation
NONcyclicphotophosphorylatio
n
cyclicphotophosphorylatio
n
ATP
NADP
• Electron Transport Chain • like in cellular respiration
– proteins in organelle membrane – electron acceptors
• NADPH
– proton (H+) gradient across inner membrane• find the double membrane!
– ATP synthase enzyme
Light reactions H+H+
H+H+
H+H+
H+H+
H+H+
H+
H+H+
H+H+
H+H+
H+H+
H+H+
H+ATP
thylakoidchloroplast
Photosynthesis summary 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?…stay tuned for the Calvin cycle
Practice Questions
• Q 1-8 p.166
Light Independent Reactions-Calvin Cycle
• Occurs in the stroma of the chloroplast.
• Where CO2 is “fixed” into sugars!
The stages of photosynthesis…
The Calvin CycleWhoops! 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
+ water + energy glucose + oxygencarbondioxide
6CO2 6H2O C6H12O6 6O2light
energy + ++
Light reactions
• Convert solar energy to chemical energy–ATP
–NADPH
• What can we do now?
energy
reducing power
build stuff !!
photosynthesis
ATP
How is that helpful?
• Want to make C6H12O6
– synthesis– How? From what?
What raw materials are available?CO2
C6H12O6
NADPH
NADPreduces CO2
carbon fixation
NADP
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
stroma
thylakoid
ATP
starch,sucrose,cellulose& more
1C CO2
Calvin cycle
5CRuBP
3C
RuBisCo
1. Carbon fixation
2. Reduction
3. Regenerationof RuBP
ribulose bisphosphateribulose
bisphosphate carboxylase
6 NADP
6 NADPH 6 ADP
6 ATP
3 ADP
3 ATP
usedto make
glucose
3C
3CG3Pglyceraldehyde-3-P
C C C C C
C C C C C
C C C C C
6C
C C C C C C
C C C C C C
C C C C C C
C C C
C C C
C C C
C C C
C C C
C C C
PGAphosphoglycerate
C C C
C C C
C C C
C C C
C C C
C C CC C C
CC
C
C C C= =
|H
|H
|H
|H
|H
|H
C C C– –
5C
glycolysis
glucoseC-C-C-C-C-C
fructose-1,6bPP-C-C-C-C-C-C-P
DHAPP-C-C-C
G3PC-C-C-P
pyruvateC-C-C
ATP2
ADP2
ATP4
ADP4
NAD+22
Remember G3P?
glyceraldehyde3-phosphate
Photosynthesis
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
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 NADPADP
Light Reactions
O2
H2O
Energy BuildingReactions
ATP
produces ATP produces NADPH releases O2 as a
waste product
sunlight
H2O ATP O2light
energy ++ + NADPH
NADPH
Calvin Cycle
sugars
CO2
SugarBuilding
Reactions
ADP
builds sugars uses ATP &
NADPH recycles ADP
& NADP back to make
more ATP & NADPHATP
NADPH
NADP
CO2 C6H12O6 ++ + NADPATP + NADPH ADP
Putting it all togetherCO2 H2O C6H12O6 O2
lightenergy + ++
SugarBuilding
Reactions
Energy Building
Reactions
Plants make both:energy
ATP & NADPHsugars
sunlight
O2
H2O
sugars
CO2
ADP
ATP
NADPH
NADP
H2O
Energy cycle
Photosynthesis
Cellular Respiration
sun
glucose O2CO2
plants
animals, plants
ATPThe Great Circleof Life,Mufasa!
CO2 H2O C6H12O6 O2light
energy + ++
even thoughthis equation
is a bit of a lie…it makes a better story
CO2 H2OC6H12O6 O2ATP
energy+ ++
Summary of photosynthesis
• 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?
6CO2 6H2O C6H12O6 6O2light
energy + ++
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
The poetic perspective…
• All the solid material of every plant was built by sunlight out of thin air
• All the solid material of every animal was built from plant material
Then all the plants, cats, dogs, elephants & people …
are really particles of air woven together by strands of sunlight!
sunair
Practice Questions
• Q 9-13 p.166