THEORY OF ABIOTIC SYNTHESIS: MAIN CHARACTERISTICS - BIOLOGY - 2024

The Abiotic Synthesis Theory is a postulate that proposes that life originated from non-living compounds (abiotic = non-living). It suggests that life gradually arose from the synthesis of organic molecules. Among these organic molecules, amino acids stand out, 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. Each of these scientists, investigating on their own, arrived at 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.

John Haldane, one of the promoters of the Abiotic Synthesis Theory

What does it consist of?

The Abiotic Synthesis Theory establishes that the origin of life on Earth was due to the mixture between inorganic and organic compounds found in the atmosphere at that time, which was loaded with hydrogen, methane, water vapor, carbon dioxide and ammonia.

Oparin and Haldane theory

Oparin and Haldane thought that the early 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 gradually change 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, the heat of the Earth's core, among other types of energy that ultimately 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 broth" the conditions would be suitable for the building blocks to have been combined in subsequent reactions.

- Larger and more complex molecules (polymers) such as proteins and nucleic acids were formed from these reactions, probably favored by the presence of water in pools 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 proteins grouped together to carry out metabolism, and Haldane suggested that the macromolecules became enclosed in membranes to form cell-like structures.

Considerations on the theory

The details on this model are probably not quite correct. For example, geologists now believe that the early atmosphere was not shrinking, and it is unclear 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 at the core of most hypotheses of the origins of the actual life.

Experiments supporting the abiotic synthesis Theory

Miller and Urey experiment

In 1953, Stanley Miller and Harold Urey did an experiment to test the ideas of Oparin and Haldane. They found that organic molecules could be produced spontaneously under reducing conditions similar to those of the early Earth described earlier.

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

To simulate the lightning bolts that could have provided the energy needed for the chemical reactions that resulted in the more complex polymers to occur, Miller and Urey sent electrical discharges through an electrode in their experimental system.

Miller and Urey experiment

After running the experiment for a week, Miller and Urey discovered that various 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 building blocks of these molecules could form spontaneously from simple compounds.

The experiment of Juan Oró

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

Oró replicated 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 adenine molecules, 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 had not only a scientific but also a popular impact, since it demonstrated the possibility of the spontaneous appearance of nucleotides on the early Earth without any external influence.

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

Sydney Fox experiment

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

Using a dry mixture of amino acids, they proceeded to heat them to 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 microspherules had a permeable double envelope, similar to current cell membranes, which allowed them to hydrate and dehydrate depending on changes in the environment where they were.

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

Alfonso Herrera's experiment

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

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

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 named these microspheres colpoids.

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