5. Photosynthesis (Chap. 10)
Transcript of 5. Photosynthesis (Chap. 10)
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C
hapter
10
-
P
hot
osyn
thes
is
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How can sunlight,
seen here as a spectrum of colors in a rainbow,
power the synthesis of organic substances?
*rainbow
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lf-feeding/make own food-producers (organicsfr. CO2 & inorganics)hotoautotrophic/chemo-
autotrophic-plants, algae, someprotists &bacteria
- feed on others-consumers (includingdecomposers)
- animals, fungi & many bacter
-dependent of photoautotrophs
food
Autotrophic vs.
Heterotrophic
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The major site ofphotosynthesis
, and specifically occur in
osynthesis occurs in all green parts of a
Chloroplasts,
Chlorophyll
- green pigment in chloropl
- absorbs light energy for
- found primarily in mesoph
leaves
O2 + 6H2O + light energy C6H12O6 + 6O2
Figure 10.3 Tracking atoms through photosynthesis
6CO2 + 12H2O + light energy C6H12O6 +
6O2 + 6H20
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- CO2 enters O2 exit
throughstomata.
These closewhen the
Transports waterand food
*leaf cross section
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Photosynthetic pigments
are found in the
thylakoid membrane.
Stacks of thylakoidmembranes are grana.
Stroma is the dense fluid
in the chloroplast.
*chloroplast
AKA
thylakoid
lumen
Leaf cross section
Vein
Mesophyll
StomataCO2 O2
ChloroplastMesophyll cell
Outer
membrane
Intermembrane
space5 m
Inner
membrane
Thylakoid
space
Thylakoid
GranumStroma
1 m
Leaf
Mesophyll
Chloroplast
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How does photosynthetic prokaryotes (bacteria), which lack
chloroplasts, go through photosynthesis?
Have chlorophyll built into plasma membrane or vesicles
Respiration Photosynthesise- from H (in glucose) trans-
ported to oxygen to make
H2O
water split & e- w/ H+ trans-
ferred to CO2 to make sugar
is redox processwhere energy is
from the oxidation of sugar to
form ATP.
exothermicreleased
is redox processwhere energy is to
reduce carbon dioxide to form
sugar.
endothermic required
Respiration vs.
Photosynthesis
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Photosynthesis can be summarized as the
following equation:6 CO2 + 12 H2O + Light energyC6H12 O6 + 6 O2 + 6 H2O
Chloroplasts split H2O into hydrogen and oxygen,
incorporating the electrons of hydrogen into sugar molecules
Reactants: 6 CO2
Products:
12 H2O
6 O26 H2OC6H12 O6
*Photosynthesis equation
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Light Reactions Calvin Cycle
-convertslight energy tochem
energy inATP & NADPH
- occur inthylakoid membranes
-reduce NADP+(adding 2 e- &
1p+)to NADPH + H+
(nicotinamide adeninedinucleotide phosphate)
- splits H2O, giving off O2
-make ATP throughphotophos-
phorylation
-carbon fixationconvert
CO2 to sugar G3P
- occurs instroma
-AKAdark orlight-independent
rxns
-NADPHprovides reducingpower (adds e- to CO2)
- ATPprovides chemical
energy
2 stages of photosynthesis are:
- returns ADP, Pi, &
NADP+ to light rxns
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Light
H2O
Chloroplast
LightReactions
NADP+
P
ADP
i+
*photosynthesis - light reactions 1
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Light
H2O
Chloroplast
LightReactions
NADP+
P
ADP
i+
ATP
NADPH
O2
*photosynthesis - light reactions 2
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Light
H2O
Chloroplast
LightReactions
NADP+
P
ADP
i+
ATP
NADPH
O2
Calvin
Cycle
CO2*photosynthesis - light reactions 3
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Light
H2O
Chloroplast
LightReactions
NADP+
P
ADP
i+
ATP
NADPH
O2
Calvin
Cycle
CO2
[CH2O]
(sugar)
*photosynthesis - light reactions 4
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*electromagnetic
spectrum
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Shorter wavelength Longer wavelength
Higher energy Lower energy
Wavelength is distance between crests.
Photons have a fixed quantity of E, even
though not discrete particles.
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*determining an
absorption spectrum
Chl h ll
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Chlorophyll a
Chlorophyll b
Carotenoids
When photon is absorbed,color disappears
e- is elevated to orbital w/
more potential E
(fr. ground to
excited state, higherorbital)
E is = to diff betw ground
& excited state,
thus each pigmentabsorbs only
photons w/ specific
wavelengths
When e- drops back toground state, HEAT.For chlorophyll a
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(a) Excitation of isolated chlorophyll molecule
Heat
Excited
state
(b) Fluorescence
PhotonGroundstate
Photon(fluorescence)
Energy
ofelec
tron
e
Chlorophyll
molecule
*fluorescence
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Englemannselegant
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Englemanns elegant
experiment:
He established thatonly certain
wavelengths of light
stimulate
photosynthesis.
Used prism to break
up light.
In areas withsuccessful
photosynthesis, O2
production increased
and bacteria grew.
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Photosystem - Light gathering unit of photosynthesis
(thylakoid membrane & proteins)
Light Reaction
t hl h llt hl h ll
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photon
transfer of
energy
rxn
center
Primary e- acceptor:Primary e- acceptor: this molecule traps excited
e- so doesnt go
back to ground state
& release E energy stored in trapped e-
makes ATP &
NADPH
rxn center chlorophyll a:rxn center chlorophyll a:special molecule that can transfer
excited e- to start light rxnsp700 for Phosys I, p680 for
Phosys II - identical but
each w/ diff protein
A photosystemA photosystem
e- transfer
antennaantenna
(accessory)(accessory)
moleculesmoleculesfew hundred pigments
(a, b, carotenoids)absorb photons & pass E
to rxn center
chlorophyll
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THYLAKOID SPACE(INTERIOR OF THYLAKOID)
STROMA
e
Pigmentmolecules
Photon
Transferof energy
Special pair ofchlorophyll amolecules
Thylako
idmembrane
Photosystem
Primaryelectronacceptor
Reaction-centercomplex
Light-harvesting
complexes
*photosystem
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ow noncyc c
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ow noncyc celectron flow during
the light rxnsgenerates ATP & NADPH
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1. Photosystem II absorbs light e- excited in P680 captured
by primary electron acceptor (need to fill e- hole)
2. Missing e- from chlorophyll a replaced by splitting of water -this is how O2 is formed
3. Excited e- pass from Photosys II to Photosys I by ETC
4. As e- go down chain, ATP is produced by phosphorylation
(just like in cellular respiration)P680P700123456Photosystem IIPhotosystemI2 H++ H2O
1/2 O2
2e-2e-primary-acceptorprimary-acceptor
PqcytochromcomplexPcATPNADP+Reductas
Fd2e-2e-NADP++
2 H+
NADPH
+ H+
2e-
PhotosystemII
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P680P700123456Photosystem IIPhotosystemI2 H++ H2O
1/2 O2
2e-2e-primary-acceptorprimary-acceptorPqcytochromcomplexPcATPNADP+ReductasFd2e-2e-NADP+
+
2 H+
NADPH
+ H+
2e-
5. At bottom of ETC, the e- fills hole in P700 replacing
excited e- of Photosys I
6. Excited e- passed to ferrodoxin (Fd) then to NADP+
forming NADPH
Photosyste
m I
Linear vs Cyclic Electron
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- conc. of NADPH may regulate which pathway is active
More NADPH than ATP
Less NADPH than ATP
Linear vs. Cyclic ElectronFlow
Pushes e- from water
(low potential E) toNADPH (high potential E)
Thylakoid membrane
converts light E to
chemical E stored inNADPH and ATP in =
quantities
Uses photosystem I but not
photosytem IIGenerates ATP, Does NOT
produce NADPH or O2
Evolved before linear flow to
protect from light induced
damage
Makes up the difference from
Calvin cycle since CC
consumes more ATP than
NADPH
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cyclic
linear
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Chemiosmosis
mitochondria
chloroplast
similarities differences
e- are passed thruseries of carriers that
are progressively
more electronegative
establishes H+
gradient to increase
potential E
ATP synthase
couples H+ diffusion
to phosphorylate
ADP
Oxidative phosphorylation
e- are extracted fr. food
fr. intermembrane spaceto matrix
Photophosphorylation
e- driven to top of chain fr.
captured light energy
fr. thylakoid space (pH 5)
to stroma (pH 8)
Mit h d i Chl l
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*ATP synthase
Key
Mitochondrion Chloroplast
CHLOROPLAST
STRUCTURE
MITOCHONDRION
STRUCTURE
Intermembrane
space
Inner
membrane
Electrontransport
chain
H+
Diffusion
Matrix
Higher [H+]
Lower [H+
]
Stroma
ATPsynthase
ADP + P iH+
ATP
Thylakoid
space
Thylakoid
membrane
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*graphic of photosystem II & I
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ATP & NADPH produced in light reaction are used in CC
- ATP is energy source- NADPH is reducing agent that adds high energy e- to
form sugar
carbon enters as CO2 and leaves as sugar (G3P)
-G3P is raw material used to make glucose & other
carbos
to make one molecule of G3P, 3 CO2 must enter CC,
and 9 ATP & 6 NADPH used
to make 1 molecule of C6H12 O6, 18 ATP & 12 NADPH are
used
Calvin Cycle Notes
*graphic of CalvinCycle
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Rubisco
Enzyme - one of
the most abundant
proteins on Earth
Occurs in
stroma
Forms unstable
6C molecule -
immediately splitsinto 2 3C molecules
3-Phosphoglycerate6 ATP
6 ADP
1,3-Biphosphoglycerate
6 NADPH
6 NADP+
6 Pi
Glyceraldehyde 3-phosphate(G3P)
more potential
energy
G3P
(to sugar)Glucose & other
organic compounds
5 G3P
series of rxns
rearranges carbon
skeleton
3 ATP
3 ADP
Ribulose Biphosphate
(RuBP)
18 ATP & 12 NADPH used
to make glucose!
y
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- opposite of photosynthesis
fostered by hot, dry, bright days when stomata closes to
prevent dehydration by reducing water loss so O2
accumulates
occurs b/c active site of rubisco can accept both O2 & CO2
photo b/c occurs in light when PS reduces CO2 & raises
O2 in leaf space, respiration b/c consumes O2,
releases CO2
produces no ATP, decreases PS output by as much as 50%
limits damaging products of light reactions that build up in the
absence of the Calvin cycle
Photorespiration
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C3 Plants
Named because first organic product of carbon
fixation is a 3C molecule (3-phosphoglycerate)
include rice, wheat, soybeans
Produce less food when their stomata close onhot, dry days.
As O2 exceeds CO2, rubisco adds O2 instead
of CO2, forming a 2C molecule that getsbroken down by peroxisomes into CO2.
If less CO2, then cant feed Calvin
Cycle.
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C4
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Named because first organic product of carbon
fixation is a 4C moleculeAre members of grass family incl. sugarcane &
cornCO2 is fixed to PEP (phosphoenolpyruvate) by
PEP carboxylase (has a highaffinity to CO2 therefore fixes CO2 more
efficiently than rubisco) in the mesophyllcells
Bundle-sheath cell performs Calvin cycleadaptive b/c enhances carbon fixing under
C4Plant
s
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CAM Plants
Named because crassulaceae
is plant family thatperforms crassulaceanacid metabolism (CAM)
In succulent (H2O-storing)
plants like cacti &pineapples.
Performs same 2 steps as in C4 plants,but occurs in same part of plant atdifferent times of day
d ti i id diti
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