PRIMORDIAL SOUP

By Sean Henahan, Access Excellence

LA JOLLA- In a simulation of the days when the Earth was covered in primordial ooze, researchers at the University of California, San Diego have synthesized pantetheine, an ingredient considered essential for the development of life on the planet.

The nature of the origin of life remains one of the most intriguing questions in biology. Researchers at the University of California, San Diego's Specialized Center of Research and Training in Exobiology are approaching the question by simulating environmental conditions as they are thought to have existed in "prebiotic" times. The researchers are studying the abiotic synthesis of biomolecules to determine which ones could have been present on Earth before life arose and, thus, may have been important to the first living organisms.

The UCSD research team is led by Dr. Stanley Miller. Dr. Miller is well known for his 'primordial soup' experiment conducted in 1953. At that time he demonstrated that amino acids could be formed by passing an electric current through a flask of methane. This suggested that life could have arisen from materials and conditions present in early Earth history.

Dr. Miller believes many other chemicals in addition to amino acids would have to have been present to facilitate the transition to living organisms. In particular, the presence of pantetheine could have enhanced the transition process. Pantetheine is related to coenzyme A, an essential component for protein formation. Coenzyme A is used by every known organism to assist in a wide variety of chemical reactions and it is possible that in the very earliest organisms this role was played by pantetheine alone, notes Miller.

In their recent experiment, the UCSD scientists heated a mixture of pantoyl lactone, beta- alanine and cysteamine at 40 degrees C (105 degrees F). All three chemicals are believed to have been present on the early Earth. Among the other chemicals formed was pantetheine. This suggests pantetheine could have been created at the margins of evaporating pools of water in prebiotic times.

"These components are extremely soluble and so would have been preferentially concentrated in evaporating bodies of water, for example on beaches and at lagoon margins. Our results show that amide bonds can be formed at temperatures as low as 40 degrees C, and provide circumstantial support for the suggestion that pantetheine and coenzyme A were important in the earliest metabolic systems," noted Miller.

There are two main hypotheses regarding the prebiotic synthesis of coenzymes. One, the "RNA world" hypothesis, holds that coenzymes were part of the covalent structure of RNA, and assisted in the RNA-based metabolism. Another hypothesis suggests that the RNA world was preceded by a thioester world. According to that hypothesis, coenzyme A played an essential role in the activation of amino acids and hydroxy acids in peptide synthesis.

The research provides evidence for the presence of an important ingredient in the original soup of life. It has been demonstrated that amino acids can form abiotically in a number of ways and are used by modern organisms for the manufacture of proteins. Sugars, however, which are components of modern genetic materials such as DNA or RNA are thought to be too unstable to have been widespread on Earth before life arose. Another of the remaining "big questions" is how and when did non-living molecules turn into life forms and begin to make copies of themselves.

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Primordial Soup

Any discussion on the origin is life is not complete without considering the primordial soup. There is no direct evidence of the soup’s existence, and on purely theoretical ground it should not exist. If it did exist, science can say with certainty that it was a very localized existence. That is it may have been a small puddle, near a volcano, right at the entrance of a cave, near an ocean or a river. The primitive ocean was definitely not the primordial soup. The ocean could not possibly serve as the soup because it would dilute the biological precursors, and it would not protect the precursors from ultraviolet light.

   Many authors have criticized the concept of the soup. Its resilience in biology text books is quite amazing given that so few scientists believe that it ever existed.

"Accordingly, Abelson(1966), Hull(1960), Sillen(1965), and many others have criticized the hypothesis that the primitive ocean, unlike the contemporary ocean, was a "thick soup" containing all of the micromolecules required for the next stage of molecular evolution. The concept of a primitive "thick soup" or "primordial broth" is one of the most persistent ideas at the same time that is most strongly contraindicated by thermodynamic reasoning and by lack of experimental support." - Sidney Fox, Klaus Dose on page 37 in Molecular Evolution and the Origin of Life.

"the primitive ocean was steadily irradiated with a relatively high dose of solar ultraviolet light . . . A steady irradiation of a rather homogeneous solution results in degradative rather than synthetic reactions" Sidney Fox, Klaus Dose in Molecular Evolution and the Origin of Life.

"Based on the foregoing geochemical assessment, we conclude that both in the atmosphere and in the various water basins of the primitive earth, many destructive interactions would have so vastly diminished, if not altogether consumed, essential precursor chemicals, that chemical evolution rates would have been negligible. The soup would have been too dilute for polymerization to occur. Even local ponds for concentrating soup ingredients would have met with the same problem.Furthermore, no geological evidence indicates an organic soup, even a small organic pond, ever existed on this planet. It is becoming clear that however life began on earth, the usual conceived notion that life emerged from an oceanic soup of organic chemicals is a most implausible hypothesis. We may therefore with fairness call this scenario the myth of the prebiotic soup." - Thaxton, Bradley, Olsen on page 66 of The Mystery of Life's Origin.

“Contrary to earlier suggestions that essentially all stages of chemical evolution occurred in the open seas, it is now generally accepted that the concentration of the soup was probably too small for efficient synthesis......”- Nissenbaum, Kenyon, Oro, in the “Journal of Molecular Evolution,” 1975.

Furthermore, any organic compounds not destroyed by UV light would react to form an insoluble polymer. This reaction known as the Maillard reaction would remove most of the organic molecules in the soup making them unavailable for chemical evolution.

“ The rapid formation of this insoluble polymeric material would have removed the bulk of the dissolved organic carbon from the primitive oceans and would thus have prevented the formation of the organic soup.” - Nissenbaum, Kenyon, Oro, Journal of Molecular Evolution, 1975.

   In summary: 1) It is extremely difficult to create information and knowledge before life exists. 2) Excessive

investigator interference is required to make biological subunits polymerize. 3) The prebiotic synthesis of the subunits required for DNA and RNA (especially ribose and cytosine) presents some very serious challenges. 4) It is unlikely that any single chemical can possess the required knowledge to replicate, because it must not only know how to replicate, but it must also know how to use an energy source to drive its own replication. 5) Any favorable environment for chemical evolution would have been highly localized to a small puddle. 6) Because of the localized nature of the soup and the low concentration of biological precursors, any robust self replicating system (i.e. Life) would need the ability to synthesize many of the chemicals required for self replication. Any self replicating system lacking this capability would not be able to survive much less replicate.

   Taken together the evidence suggests that the first living thing was not a self replicating molecule, but rather a system of chemicals that contained the knowledge required to replicate, and the ability to couple this replication to an energy source. Furthermore, the scarcity of chemicals like ribose, adenine, and cytosine imply that for this system to survive, it must have been able to synthesize many if not all such chemicals from more abundant chemicals. All of these factors imply that the first living thing was not that much simpler than life as it exists today. It may have even been more complex.

The primordial soup is often envisioned as an evaporating pond next to the ocean. The tides and waves continually bring new chemicals into the pond, the sun evaporates the water concentrating the chemicals, and the chemicals polymerize into things like RNA molecules. Thaxton discussed this myth at length in his out of print book: The Mystery of Life's Origin. The basic problem is that the UV light destroys biological molecules faster than it synthesizes them. And the salt in the ocean once concentrated will prevent the polymerization of organic molecules (salt causes these molecules to precipitate out of solution so that they are no longer available for polymerization).