Transcript The light reactions

Similarities between
photophosphorylation and
oxidative phosphorylation
e
H+ gradient
formation
e
Energy from
electrons is used
for H+
translocation
H+
ATP synthesis
is driven by H+
gradient
H+ H+ H+
H+
Proton
e
pump
H+
ATP
synthase
ATP
ADP+Pi
Energy source:
electrons
NADH
FADH2
Differences between
photophosphorylation and
oxidative phosphorylation
Energy source: light
e
H+
H+
H+
H+
H+
Proton
pump
O2
H+
NADP+
ATP
ATP
synthase
+
H
H
O
2
ADP+Pi
By-product:
NADPH
water
By-product: electrons
Photosynthesis:
The light reactions
(photophosphorylation)
Chlorophyll (or other pigments) absorbs light energy and conserve it
as ATP and NADPH.
Not all photosynthetic organisms use H2O as electron donor in
photosynthesis; thus not all of them produce O2 while they produce
ATP and NADPH.
There are two types of photosynthesis: oxygenic (producing
oxygen) photosynthesis and anoxygenic (not producing oxygen)
photosynthesis. Only organisms with two photosystems can do
oxygenic photosynthesis.
At lease half of the photosynthsis in this world is done by
microorganisms (algae, photosynthetic eukaryotes and photosynthetic
bacteria).
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Thylakoid membrane
(lamellae)
Outer membrane
Inner membrane
lumen
stroma
grana
Chloroplast has photosystems with closely
arranged chlorophyll
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Cyanobacteria & red algae also contain similar
structures called phycobilisome to facilitate light
absorption
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The major light absorbing
pigment in higher plants
Alternating single
and double bonds
give strong
absorption in the
visible light
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The accessory pigment in
bacteria and algae
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What wavelength of light
chlorophyll absorbs?
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Chlorophylls can cover part of
the spectrum – blue and red
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The part of
spectrum covered
by chlorophylls
coincides with the
action spectrum of
photosynthesis
Accessory pigment: the red-orange -carotene
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Accessory pigment: lutein (the red-orange
isoprenoid)
-carotene and lutein can help
plant absorb more light
Phycoerythrin and phycocyanin
can absorb light that other
pigments cannot absorb
Anoxygenic photosynthesis
(ferredoxin)
(pheophytin)
(restore RC
to original
state)
(restore RC to original state)
(PSII)
(PSI)
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The Z scheme of oxygenic photosynthesis
(special form of chlorophyll)
(phylloquinone)
(pheophytin)
(plastoquinone)
Green bacteria type
Purple bacteria type
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(A1)
PSI and PSII on thylakoid membrane are
separated to prevent Excition Larceny
LHCII holds
grana together
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Granal stacking by LHCII is regulated by
light intensity
ATP
LHCII
Pi
-Thr-OH
-ThrP
ADP
nonappressed
appressed
Protein
kinase
PPase
Low
High light
light
[PQH2]
[PQ]
Cytochrome b6f complex
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Oxidative phosphorylation and
photophosphorylation has
something in common in
cyanobacteria
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D1
D2
QA
QB
Fe
Pheo
Pheo
e
e
P680
Tyr
e
e
Mn
e4H
+e
O
e2
Mn
e Mn
e
Mn
2H2O
Oxygen-evolving complex
(water-splitting complex)
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N
P
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N
N
N
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bacteriorhodopsin
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All-trans-retinal
Proton transport
13-cis-retinol
Chloroplast from
higher plants is
probably evolved
from endosymbiotic
bacteria
(prochlorophytes)
Chloroplast from red algae is
probably evolved from
cyanobacteria
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