The light harvesting complex LHC viewed from above' The trimeric LHC captures photons and delivers t

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The light harvesting complex (LHC) viewed
from above. The trimeric LHC captures photons and
delivers them to Photosystem II. Two subunits
show their chlorphylls and carotenoids in green.
space Photosystem II, viewed in the plane
of the membrane, uses light to turn water into a
reductant and, in the process, liberate
electrons, molecular oxygen, and protons. Each
protein subunit is depicted by a unique color.
Chlorophyll molecules are in rendered in
green. space Cytochrome b6f complex, accepts
electrons from PSII via quinones (Q) and
transports protons into the lumen. space
Photosystem I accepts electrons from plastocyanin
(PC), energizes them, and reduces ferredoxin (Fd)
ultimately yielding NADPH. space F0F1 ATP
synthase is a multisubunit molecular machine that
rotates as it consumes proton motive force and
synthesizes ATP.
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Photosyntheic microorganisms dominate!
Provided by the SeaWiFS ProjASA/Goddard Space
Flight Center and ORBIMAGE
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From Atoms to Planets, Picoseconds to
Eras Photosynthesis, a fundamental biological
process
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http//visibleearth.nasa.gov/
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Human activities and global warming
ice core measurments of atmospheric
CO2 cycles correlate with ice ages
average temperature deviation over last 150 years
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Biological energy conversion
Photosystem II (Natures Solar Energy
Converter) H2O O2
Cytochrome c Oxidase (Natures Fuel Cell) O2
H2O
chloroplasts
mitochondria
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6 CO2 6 H2O --gt C6H12O6
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Photosynthesis
Photosynthesis
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Direct biophotolysis
reducing power generated by photosynthetic
apparatus used to reduce protons to
H2 continuous production of H2 in the
light hydrogenase is inhibited by O2 produced by
PSII
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Uptake hydrogenase
consumes H2 produced by nitrogenase offsets
cost of N2 fixation
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Bidirectional hydrogenase
can also consume H2, reducing power stored in
NADH used to dump excess reducing power,
protons reduced to H2 gas
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Indirect biophotolysis
reducing power is used to first fix inorganic
carbon carbohydrates act as storage medium for
hydrogen (C6H12O6 with H2O theoretically yields
12 H2) reducing energy and hydrogen are released
by fermentation O2 generating and O2 sensitive
processes are temporally separated
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Photofermentation
light is used to excite electrons donated by
organic acids (breakdown products of
sugars) reducing power used by nitrogenase and
H2 is liberated requires feedstock from other
sources (biomass, wastes, co-cultured organisms)
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Dark fermentation
organic matter is fermented to H2 anaerobic
bacteria mixed cultures feedstock
production/consumption not linked
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Human activities and global warming
Keeling curve shows trend of increasing CO2
occurring over 4 decades seasonal variation in
northern hemisphere due to vegetation amount of
CO2 increase from 280 ppm (pre-1860) to 370 ppm,
at present increase of 30 ppm in last 20 years
alone see Carbon Cycle Greenhouse Gasses Group
at NOAA (http//www.cmdl.noaa.gov/ccgg/index.htm
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H2- an ideal energy carrier
can be stored, shipped, and used multiple
sources sustainable if renewable source is used
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Photosynthesis
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Outline of electron and proton movement in
photosynthetic architecture
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Simpleschematic for biological hydrogen
production
other examples include open ponds for the
accumulation and harvesting of algal biomass
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Real world photobioreactor
from Photosynthetic Prokaryotes, Mann and Carr,
eds.
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