BY DR. JOSE PALU-AY DACUDAO
(Why Chernobyl mammalian wildlife survive)
FOR THE curious reader, photosynthetic plants can make all 20 or so amino acids needed for protein synthesis from carbon dioxide, nitrogen, sulfur. Most of other organisms cannot synthesize all of them, and thus must derive them from food or other sources.
For us humans, that is true for nine amino acids, which are therefore called essential amino acids. Humans have to ingest them from food sources in order to make proteins. Our bodies’ collagen, muscles, enzymes and so on are all proteins.
There are nine essential amino acids for humans – histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine.
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Less known is that phenylalanine is a catabolic byproduct of the artificial sweetener Aspartame, which can cause Phenylketonuria among patients that lack an enzyme needed in phenylalanine catabolism. Phenylalanine is even less known as a precursor of the amino acid tyrosine which in turn is the precursor of the neurotransmitters dopamine and norepinephrine.
What is almost unknown known is that phenylalanine is the most commonly synthesized amino acid in the biosphere. Plants synthesize it in gargantuan amounts as a precursor to lignin.
This rather complicated process of lignin-making in plants is one of the most massive biological activities in the entire biosphere, as about 30% of the biomass in the world is lignin. People that crave to remove carbon dioxide from the atmosphere may also cheer this, and every woody tree and shrub makes it.
Lignin is also by far the most plentiful biologically hard-to-decompose organic materials on our planet. Why?
Lignin is composed of cross-linked polymers of aromatic phenols (carbon-chains arranged in a ring), stacked up on top of each other. This makes lignin insoluble in water and even hydrophobic, and this protects its innards from water borne enzymes (meaning all enzymes).
A microbe needs to introduce enzymes dissolved in water into a substance in order to decompose it. (That’s why wood stays as wood for a long time, compared to leaves made of cellulose and hemicellulose, which decompose quickly.)
In addition, lignin is extraordinarily rich in carbon. Lignin (oft-quoted approximately as C31H34O11) is made up by atoms of almost equal parts of carbon and hydrogen, with oxygen just one third of the carbon.
Note that glucose C6H12O6 only has equal parts of carbon and oxygen atoms and with hydrogen atoms double the number of carbon atoms. Thus, it takes a lot of carbon dioxide, which the plant has to take from the atmosphere, to make lignin.
When photosynthesis makes lignin and the lignin does not decompose or is burned, carbon dioxide is taken away from the atmosphere and is not emitted back, as seen in the equation:
6 CO2 + 6 H2O (water) → C6H12O6 (organic substance, which eventually becomes lignin, C31H34O11, after oxygen and hydrogen atoms are removed from it in the plant’s metabolic processes) + 6 O2 (oxygen) (To be continued)/PN
