JTW's Evolutionary Origins - Author: Wood, John T.

The Point of Origin for A CAT Metabolism in OOL

The origins of the planet and the origins of life are inextricably linked, the geochemistry of Earth's early formation and equilibration initiating and driving the very chemical system that would propel biological life forward in time.

Today's Biosphere, and the organisms that comprise it, are the result of a primordial chemical reaction system that has a minimal three and a half billion year history, more likely closer to four billion years.

The system has been evolving thru a continuous series of chemical transformations that regenerate it's core constituents and as well as generating a diverse repertoire of novel secondary metabolites products as well.

The dynamic turnover and transformation of organic constituents is at the heart of this reaction system.

It has become clear that the patterning of Life's foundations (at least for biological life) rest on chemical principles derived from the interaction of a very specific subclass of organic constituents and their catalysts, ie CHNOPS and select Alkali (Na, K), Alkaline Earth (Ca, Mg), and transition metals (Fe, Ni, Co, Mo, Mn, Cu, Zn, etc...).

The metabolic heart or core that maintains life's essence can be traced in most organisms to a few central chemical pathways that ensure the energetic and structural needs of the organism are met.

These pathways provide the necessary autocatalytic components that keep the reaction system viable and prevent its dissolution to the constituents favored by thermodynamic equilibrium.

Key players in this process are the Glycolysis/Gluconeogenesis pathway, Oxidative/Reductive Citric Acid Cycle, The Pentose Phosphate Shunt, and the Amino Acid pathways.

Crucial to the autocatalytic nature of these pathways is the presence of highly conserved coenzymes and cofactors present in the enzymes that catalyze the reactions within these pathways.

Together, these pathways and coenzyme/cofactors, provide the necessary materials (sugars, amino acids, nucleotides, and fatty acids) for the formation of the building blocks of the polymers that are the defining componets of "Biological Life": Carbohydrates, Proteins, Nucleic Acids, and Lipids.

While these components are not absolutely necessary for the evolution of sustained organic chemical reaction systems, in biological systems, they serve the central role of producing and stabilizing the recurrent patterning of the biochemical reaction system and its expansion via the fissioning and spinning off of degenerate reproductions of the reaction system core.

Building a chemoautotrophic (CAT) metabolism exhibiting the universal features of extant metabolisms is no easy intellectual task.

By definition, a CAT metabolism must be built from scratch.

The starting materials are drawn from the flux of matter and energy that were present at the point of origin.

Fossil evidence and radiometric dating lead us to believe that the point of origin was the Archean Earth, circa 3.9-3.5 billion years ago.

At this point in time, the early earth was in the process of moving towards mechano-chemical equilibrium after the turbulent processes of solar system and planetary formation.

Early on, geological processes reached a relative dynamical equilibrium, as the basic features of the planetary crust, mantle, and core (the "Geosphere") were established.

Atmospheric and surface conditions would have to wait until the bombardment of massive impactors had slowed to a trickle.

These impactors were primarily derived from debris left over from the formation of the solar system.

Occasionally this material was supplemented with material of extra-solar origin (outside the "Heliosphere") and other interstellar debris.

Early on, these bodies ranged in size from relatively large proto-planets to individual molecules.

Any body captured by the Earth's gravitational field became a part of the influx.

Only the lighter materials, such as hydrogen, were able to gain the escape velocities necessary to return to space.

Even today, a significant quantity of organic and inorganic material is added to the Earth's bounty.

Four billion years ago this influx was much greater by at least several orders of magnitude.

The last of the great impactors, those with enough mass and energy to boil away the earths early oceans, arrived around 3.9 billion years ago.

This is the beginning of our four hundred million year long window of oppurtunity, that is, this is the earliest that an aqueous reaction system could have emerged and persisted into modern times with no breaks in the continuity of it's aqueous environment (unless the system was able to persist in the dehydrated state or within a vaporized droplet).

Only after the largest impactors had ceased, could the oceans (or "Hydrosphere") and atmosphere begin to equilibriate with the geosphere and persist with any continuity.

Aside from occasional extraterrestrial pertubations, the earth reached a relative state of dynamic mechanical equilibrium but continued to be far from reaching chemical equilibrium.

The early earth underwent relatively drastic fluctuations in temperature as well.

These oscillations in the ambient temperature conditions play an important part in the process of evolving chemical systems.

The more so as the number of stable substances increases in number, size and complexity.

Temperature dependent phase boundaries develop between constituents, trapping one phase inside another in accordance with their physical and chemical properties, i.e. solids witin solids, solids within liquids (solutes), solids within gases (particulates), liquids within solids, liquids within liquids, liquids within gases (vapors), gases within solids, gases within liquids (solutes).

Much as metal ores form during the cooling of molten magma.

This "trapping" on one constiuent within another is a form of solvation.

Solvation usually serves to seperate potential reactants and thereby kinetically inhibit reactions (relative to the vacuum state) that are thermodynically favorable.

This is achieved via the effect of the solvent in raising the activation energy necessary to reach the transition state.

With our original goal of building a CAT metabolism in mind, it might be useful to note that extant biochemistry is metallo-organic chemistry in an aqueous solution, that is, water is the "trapping" agent, i.e. the solvent.

The organic constituents are either trapped within solvent cages of water or embedded within hydrophobic lipid bilayers.

The strong dielectric properties of water result in the kinetic inhibition of reactions between organic constituents in aqueous solutions.

Water being the major component of the system competes with substrates for potential interactions leading to the transition state.

This results in the retardation of reaction rates by increasing the activation energy barriers for the set of potential reactions.

The solvation energy is important in determining the reaction rate and therefore is also a contributer to patterns of temporal regulation in metabolic networks.

Modulation of the solvent environment around the substrates is a key mechanism for accelerating or retarding enzyme catalyzed reactions.

In a sense, the solvent transforms the systems activation energy landscape from that of the vacuum state to that of the solvent environment.

Thru catalysis the saddle points within the solvated systems activation energy topology can be lowered to somewhere between those of the solvent and those of the vacuum state.

In biochemistry, evolving enzymes have exploited this process to selectively carve out a structured network of specific metabolic reactions from the overall set of potential reactions that could occur in the vacuum state.

Once these metabolic pathways feedback upon themselves in such a way as to cyclically regenerate their original constituents, a hub has been formed.

Branch pathways the reconverge upon the hub make possible the replication of the hub.

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