The ID Report

Review Of Alexander Oparin's 'Genesis and Evolutionary Development of Life'

By Robert Deyes
ARN Correspondent

In 1924 the Russian biochemist Alexander Oparin made his mark on 'life origins' debates by proclaiming that life had sprung into existence through natural chemical processes here on earth. In Oparin's assessment, the origin of life on our planet was more than a 'lucky accident'. It was and is a phenomenon that could be studied through objective scientific research. For Oparin, the beginning of life 3.9 million years ago would have required that at least two conditions be met- an absence of free atmospheric oxygen and an abundance of ultraviolet radiation that would have allowed the formation of life-essential hydrocarbons through photochemical processes. In short, conditions would have needed to have been radically different to what they are today. Oparin's conclusions were clearly emphasized in his 1969 book 'Genesis and Evolutionary Development of Life' where he talked about the 'preactualistic era' of the earth's history. He concluded that the existence of life today 'mixed the cards' because the products of metabolism generated by living organisms would not have been present before life began. As he expounded in his book:

"[organisms] could have been formed only on the basis of a lengthy evolution through the gradual perfection of some far simpler original systems isolated from the general homogeneous solution of organic compounds"

According to Oparin, life would have had to have begun through the isolation of portions of a 'primitive soup' containing building blocks such as amino acids and nucleotides. Separation from the ravages of the external environment would have had to have been maintained by some ill-defined boundary or wall made of lipid-protein complexes; perhaps a primitive version of the membrane that forms the outer boundary of cells today. Oparin went further still by speculating that such a boundary would not only have contained a protoplasmic fluid distantly resembling the cytoplasm but would have also provided a 'frontier' for the rapid exchange of components necessary for cellular survival.

To bolster the credibility of his theory, Oparin drew on the chemistry of coacervation- a process whereby large molecules organize themselves into drop-like aggregates or 'coacervates' and which he considered as one possible avenue for the formation of cell-like units on our primitive earth. What most impressed Oparin about coacervates was that they could host simple biochemical reactions when supplied with the appropriate enzymes. Of course the simplicity of these reactions was a far cry from the highly complex network of biochemical signals and metabolic pathways that comprise the dynamics of the simplest of living cells we know of. Nevertheless one of his primary objectives was to show the fluidity of a biochemical reaction occurring within the coacervate drop. This he achieved successfully.

Through his work on coacervates, Oparin became one of the first proponents of the 'metabolism-first' approach for explaining the origin of life by suggesting that biochemical processes and not some form of genetic instruction provided the seeds for the formation of the first cell (Ref 1). Yet from the onset, Oparin's experiments faced tremendous theoretical as well as practical problems. Most notably coacervation is a process that relies solely on electrostatic attraction between molecules and has therefore very little in common with the plasma membranes of living cells (Ref 2). Moreover, the process of coacervation requires careful control of chemical parameters such as pH, temperature and salt concentrations if the necessary molecular aggregations are to occur (Ref 2)- hardly what one might expect from the chemical maelstrom of a prebiotic soup.

For a primitive membrane-like barrier to have been an effective frontier to the outside world, it must have not only been selectively permeable to molecules needed for intra-cellular biochemical reactions but also must have been capable of maintaining an osmotic equilibrium with surrounding water (Ref 3). Today organisms have active transport systems that allow them to perform precisely this function (Ref 3). These systems involve intricate arrays of transmembrane channels made of defined protein complexes none of which would have been present in a hypothetical coacervate-type cell. Ohio University chemist David Deamer has answered such an impass by asserting that life must have existed in a "low ionic strength lacustrine environment" such as a pond or lake where salts might have been more dilute (Ref 3). Yet unless such lakes were supplied with just the right amounts of water to maintain the status quo, evaporation effects would only have served to concentrate these salts.

Oparin's belief in the significance of coacervates was reflective of the knowledge of the day since during much of Oparin's life, the cell's complexity was a mystery. The molecular biology revolution had not yet occurred and so the detailed role of DNA and the functional diversity of proteins had not yet been uncovered. In keeping with Darwins' theory of evolution, Oparin and the English biochemist J.B.S Haldane inferred that cellular biochemical networks and metabolic processes could have arisen in a gradual bit by bit fashion within the context of primitive coacervate-type cells. Nevertheless they failed to consider the minimal requirements of a functional cell and the enormous jump between a structure as simple as a coacervate drop and the simplest form of life. In his review of the work of biochemist Harold Morowitz, biologist Michael Denton exposed the magnitude of the problem:

"A [self-replicating] cell would necessarily be bound by a cell membrane and the simplest feasible [membrane] would probably be the typical bilayered lipid membrane utilized by all existing cells on earth today. The synthesis of the fats of the cell membrane would require perhaps a minimum of five proteins. Energy would be required, and this might require a further eight proteins for a very simple form of energy metabolism. Altogether, probably a minimum of another hundred proteins would be required for DNA replication and protein synthesis. The size of such a cell, containing perhaps four mRNA molecules, a full complement of enzymes, DNA molecules about 100,000 nucleotides long and bounded by a cell membrane, would be about one-tenth of a micron in diameter. Morowitz comments, "This is the smallest hypothetical cell that we can envisage within the context of current biochemical thinking. It is almost certainly a lower limit, since we have allowed no control functions, no vitamin metabolism and extremely limited intermediary metabolism" (Ref 4, p.309)

In his book Oparin clearly missed the point, assuming so much while at the same time demonstrating so little about how natural processes could have lead to the first cell. Others who have followed his example have done no better.

REFERENCES
1. Richard Robinson (2005), Jump-Starting a Cellular World: Investigating the Origin of Life, from Soup to Networks, PLoS Biol, Vol 3(11), p. e396

2. Charles Thaxton, Walter Bradley and Roger Olsen (1984), The Mystery of Life's Origin Reassessing Current Theories, Published by Lewis and Stanley, Dallas, Texas, pp. 171-172

3. David Deamer, Jason Dworkin, Scott Sandford, Max Bernstein, Louis Allamandola (2002), The First Cell Membranes, Astrobiology Volume 2, pp. 371-381

4. Michael Denton (1998), Nature's Destiny: How The Laws of Biology Reveal Purpose in the Universe, 1st Edition Published by the Free Press, New York