Theory of Abiotic Synthesis: Main Characteristics

The Theory of abiotic synthesis is a postulate that proposes that life originated from non-living compounds (abiotic = not alive). It is also known as chemosynthetic theory because it suggests that life arose gradually from the synthesis of organic molecules.

Among these organic molecules are the amino acids, which are the precursors of more complex structures that give rise to living cells. The researchers who proposed this theory were the Russian scientist Alexander Oparin and the British biochemist John Haldane.

John Haldane, one of the promoters of the Theory of abiotic synthesis

Each of these scientists, investigating on their own, came to the same hypothesis: that the origin of life on Earth came from organic and mineral compounds (non-living matter) that previously existed in the primitive atmosphere.

What is it?

The Theory of abiotic synthesis states that the origin of life on Earth occurred thanks to the mixture between the inorganic and organic compounds that were in the atmosphere of that time, which was charged with hydrogen, methane, water vapor, carbon dioxide and ammonia.

Theory of Oparin and Haldane: Main characteristics

Oparin and Haldane thought that the primitive Earth had a reducing atmosphere; that is, an atmosphere with little oxygen where the molecules that were present tend to donate their electrons.

Subsequently, the atmosphere would change gradually giving rise to simple molecules such as molecular hydrogen (H2), methane (CH4), carbon dioxide (CO2), ammonia (NH3) and water vapor (H2O). Under these conditions, they suggested that:

- Simple molecules could have reacted, using energy from the sun's rays, electrical discharges from storms, heat from the Earth's core, among other types of energy that finally affected physicochemical reactions.

- This promoted the formation of coacervates (systems of molecules from which life originated, according to Oparin) that floated in the oceans.

- In this"primitive soup"the conditions would be adequate so that the building blocks could have been combined in later reactions.

- From these reactions, larger and more complex molecules (polymers) were formed, such as proteins and nucleic acids, probably favored by the presence of water from puddles near the ocean.

- These polymers could have been assembled into units or structures capable of being maintained and replicated. Oparin thought that they could have been"colonies"of grouped proteins to carry out the metabolism, and Haldane suggested that the macromolecules were encased in membranes to form cell-like structures.

Considerations about theory

The details of this model are probably not entirely correct. For example, geologists now believe that the primitive atmosphere was not shrinking, and it is not clear whether ponds at the edge of the ocean are a likely site for the first appearance of life.

However, the basic idea"a gradual and spontaneous formation of groups of simple molecules, then the formation of more complex structures and finally the acquisition of the ability to self-replicate"remains the core of most hypotheses of the origins of the actual life.

The 4 main experiments that support the Theory of abiotic synthesis

1- Miller and Urey experiment

In 1953, Stanley Miller and Harold Urey did an experiment to test the ideas of Oparin and Haldane. They discovered that organic molecules could occur spontaneously under reducing conditions similar to those of the primitive Earth previously described.

Miller and Urey built a closed system that contained a quantity of heated water and a mixture of gases thought to be abundant in the early Earth's atmosphere: methane (CH4), carbon dioxide (CO2), and ammonia (NH3).

To simulate the rays that could have provided the energy necessary for the chemical reactions that gave rise to the more complex polymers to occur, Miller and Urey sent electric shocks through an electrode in their experimental system.

Experiment Miller and Urey

After letting the experiment run for a week, Miller and Urey discovered that several types of amino acids, sugars, lipids and other organic molecules had been formed.

Large, complex molecules-like DNA and protein-were missing. However, the Miller-Urey experiment showed that at least some of the basic components of these molecules could be formed spontaneously from simple compounds.

2- The experiment of Juan Oró

Continuing with the search for the origins of life, the Spanish scientist Juan Oró used his biochemical knowledge to synthesize, in laboratory conditions, other organic molecules important for life.

Oro replied the conditions of the Miller and Urey experiment, which produces cyanide derivatives in large quantities.

Using this product (hydrocyanic acid), plus ammonia and water, this researcher was able to synthesize molecules of adenine, one of the 4 nitrogenous bases of DNA and one of the components of ATP, a fundamental molecule to provide energy to most living beings .

When this finding was published in 1963, it not only had a scientific impact but also a popular one, since it demonstrated the possibility of the spontaneous appearance of nucleotides in primitive Earth without any external influence.

He also synthesized, recreating in the laboratory an environment similar to that which existed in the early Earth, other organic compounds, mainly lipids that are part of cell membranes, some proteins and active enzymes important in metabolism.

3- Sydney Fox Experiment

In 1972, Sydney Fox and his collaborators conducted an experiment that allowed them to generate structures with membrane and osmotic properties; that is, similar to living cells, which they called Proteinoid microspheres .

Using a dry mixture of amino acids, they proceeded to heat them at moderate temperatures; thus they achieved the formation of polymers. These polymers, when dissolved in saline, formed tiny droplets the size of a bacterial cell capable of carrying out certain chemical reactions.

These microspheres had a double permeable envelope, similar to the current cell membranes, which allowed them to hydrate and dehydrate depending on the changes in the environment where they were.

All these observations obtained from the study of the microesférulas, showed an idea about the type of processes that could have originated the first cells.

4- Alfonso Herrera's experiment

Other researchers conducted their own experiments to try to replicate molecular structures that gave rise to the first cells. Alfonso Herrera, a Mexican scientist, managed to artificially generate structures that he called sulfobios and colpoides.

Herrera used mixtures of substances such as ammonium sulfocyanide, ammonium thiosyanate and formaldehyde, with which he was able to synthesize small structures of high molecular weight. These structures rich in sulfur were organized in a similar way to living cells, so he called them sulfobios.

Similarly, he mixed olive oil and gasoline with small amounts of sodium hydroxide to generate other types of microstructures that were organized in a similar way to protozoa; He called these microspheres colpoides.

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