Transcript The light reactions

Similarities between
photophosphorylation and
oxidative phosphorylation
H+
e
H+ H+ H+
H+
Proton
pump
ATP
synthase
ATP
H+
H+
ADP+Pi
Differences between
photophosphorylation and
oxidative phosphorylation
NADH
FADH2
e
H+
H+
H+
H+
H+
Proton
pump
O2
H+
H2O
NADP+
ATP
H+
NADPH
ATP
synthase
ADP+Pi
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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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The spectrum of electromagnetic
radiation
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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
(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
Cytochrome b6f complex
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Oxidative phosphorylation and
photophosphorylation has
something in common in
cyanobacteria
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Oxygen-evolving complex
(water-splitting complex)
In protein subunit D1
of the PSII reaction
center; the immediate
electron donor to
P680
can only accept one electron at a time
Loses one electron and proton at a time
to P680; electrically neutral Tyr free
radical (Tyr•) is generated
tyr• then regain its electron and proton by oxidizing four Mn
in the water splitting complex; each transfer corresponds to
one photon absorption
Here the Mn
complex takes four
electrons from a
pair of water
molecules;
releasing 4H+ and
O2
Goes to lumen
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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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