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Hydrogen
I don't have much interest in hydrogen as a fuel source over the next few decades, but it's quite a story, now that I understand the "holy grail" of energy, as it were.
It begins with photosynthesis.
There are two components:
- photosynthesis I, requires light; e.g., daylight;
- photosynthesis II, does not require light; can continue throughout the night;
Photosynthesis II requires an oxygen-evolving complex -- the complex sits at the very edge of the Photosynthesis II system itself, facing the outside world, and gives a sense of being 'tacked on.' It's shockingly small. The complex is a cluster of four manganese atoms and a single calcium atom, all held together by a lattice of oxygen atoms. And that's that.
That was from Life Ascending: The Ten Great Inventions of Evolution, Nick Lane, p. 85.
Lane goes on:
... until 2006, we did not know the structure of the manganese cluster in atomic resolution, ... but now we know ... Whether the original oxygen-evolving complex was simply a bit of mineral that got wedged in Photosystem II, we don't know ... Like a few other metal clusters found at the heart of enzymes, it is almost certainly a throwback to the conditions found billions of years ago in a hydrothermal vent. Most precious of all jewels, the metal cluster was wrapped in a protein and held in trust for all eternity by the cyanobacteria.
However it formed, this little cluster of manganese atoms opened up a new world, not only for the bacteria that first trapped it, but for all life on our planet.
Once it formed, this little cluster of atoms started to split water, the four oxidized manganese atoms combining their natural avidity to yank electrons from water, thereby releasing oxygen as waste.
Stimulated by the steady oxidation of manganese by ultraviolet radiation, the splitting of water would have been slow at first. But as soon as the cluster became coupled to chlorophyll, electrons would have started to flow.
Getting faster as chlorophyll became adapted to its task, water was sucked in, split open, its electrons drawn out, oxygen discarded.
One a trickle, ultimately a flood, this life-giving flow of electrons from water is behind all the exuberance of life on earth.
We must thank it twice -- once for being the ultimate source of all our food, and then again for all the oxygen to burn up that food to stay alive.
It's also the key to the world's energy crisis. We have no need for two photos systems, for we're not interested in making organic matter. We only need the two products released from water: oxygen and hydrogen.
Reacting them together again generates all the energy we'll every need and the only waste is water.
In other words, with this little manganese cluster, we can use the sun's energy to split water, and then react the products back together to generate water -- the hydrogen economy.
Chemists around the world are racing to synthesize this tiny manganese cluster in the lab, or something similar that works as well. Soon, surely, they will succeed.
And then it can't be long before we learn to live on water and a splash of sunshine.
Perhaps something that Sophia will see someday.
Right now, as readers tell me, it is incredibly expensive the way humans use electricity to make hydrogen.
What
amazes me is that the Japanese and Chinese are able to reverse engineer
American inventions, but American inventors are not able to reverse
engineer what nature has done.
In photosynthesis, the light-dependent reactions take place on the thylakoid membranes.
The inside of the thylakoid membrane is called the lumen, and outside the thylakoid membrane is the stroma, where the light-independent reactions take place.
The thylakoid membrane contains some integral membrane protein complexes that catalyze the light reactions.There are four major protein complexes in the thylakoid membrane:
- photosystem II (PSII);
- cytochrome b6f complex;
- photosystem I (PSI); and,
- ATP synthase.
These four complexes work together to ultimately create the products ATP and NADPH.
The four photosystems absorb light energy through pigments—primarily the chlorophylls, which are responsible for the green color of leaves.
The light-dependent reactions begin in photosystem II. When a chlorophyll a molecule within the reaction center of PSII absorbs a photon, an electron in this molecule attains an excited energy level. Because this state of an electron is very unstable, the electron is transferred from one to another molecule creating a chain of redox reactions, called an electron transport chain (ETC).
The electron flow goes from PSII to cytochrome b6f to PSI.
In PSI, the electron gets the energy from another photon. The final electron acceptor is NADP. In oxygenic photosynthesis, the first electron donor is water, creating oxygen as a waste product.
In anoxygenic photosynthesis various electron donors are used.
Photosystem I -- PSI, or plastocyanin-ferredoxin oxidoreductase -- is one of two photosystems in the photosynthetic light reactions of algae, plants, and cyanobacteria.
Photosystem I is an integral membrane protein complex that uses light energy to catalyze the transfer of electrons across the thylakoid membrane from plastocyanin to ferredoxin.
Ultimately, the electrons that are transferred by Photosystem I are used to produce the high energy carrier NADPH.
The combined action of the entire photosynthetic electron transport chain also produces a proton-motive force that is used to generate ATP.
PSI is composed of more than 110 cofactors, significantly more than Photosystem II.
Photosystem II -- or water-plastoquinone oxidoreductase -- is the first protein complex in the light-dependent reactions of oxygenic photosynthesis.
It is located in the thylakoid membrane of plants, algae, and cyanobacteria.
Within the photosystem, enzymes capture photons of light to energize electrons that are then transferred through a variety of coenzymes and cofactors to reduce plastoquinone to plastoquinol.
The energized electrons are replaced by oxidizing water to form hydrogen ions and molecular oxygen.
By replenishing lost electrons with electrons from the splitting of water, photosystem II provides the electrons for all of photosynthesis to occur.
The hydrogen ions (protons) generated by the oxidation of water help to create a proton gradient that is used by ATP synthase to generate ATP.
The energized electrons transferred to plastoquinone are ultimately used to reduce NADP+ to NADPH or are used in non-cyclic electron flow.
DCMU is a chemical often used in laboratory settings to inhibit photosynthesis. When present, DCMU inhibits electron flow from photosystem II to plastoquinone.
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