The RNA World Theory

In many ways the origin of life issue presents researchers with a three pronged chicken and egg scenario. Although my description here is very simplified, in essence DNA represents the "blueprint" for building, various forms of RNA are the constructors that build from the blueprint, and proteins are the machines the RNA "builds" - they do the majority of the cell's "work" and form its structure. The problem is which of these seemingly interdependent substances came first? At one time proteins were seen to have developed first, but since the late 1980's scientists have preferred to think of RNA as coming first. This is because RNA has been shown to have some modest catalytic properties and could perhaps act as a template for its own self-reproduction. The theory is, that stable strands of RNA formed, eventually giving rise to a self-replicating form of RNA, with the wonders of evolution and natural selection then taking over, leading through a number of steps to the formation of fully functional life forms. These steps would include the use and production of proteins to more efficiently catalyze and complete reproductive functions, as well as the use of DNA as an information template.
Although it is definitely the leading theory in its field, there are a number of serious unresolved problems with the RNA world concept. The first would be the conditions and processes under which it came to be. Christian de Duve, an expert in the field, has termed this as "the set of unknown chemical reactions that generated the RNA world and sustained it throughout its existence". The term "unknown" is a subtle euphemism that covers over a decade of failed research seeking to identify a natural process that would produce significant quantities of RNA. For example - large quantities of phosphate (an essential ingredient in both DNA and RNA) are unusual in natural waters as they tend to be tied up and precipitate out as Calcium Phosphate - an insoluble compound. It is not difficult to produce random strands of RNA in the lab - any chemist with common reagents available at any good chemical supply house could produce some with a fairly minimal effort. But that is exactly the issue: there were no chemists, reagents, labs or chemical supply houses present when life first appeared. To be plausible, the process must be one which would occur naturally and not require the use of purified reagents, oversight of a competent chemist, a set of conditions highly unlikely on the early earth, etc. The issue of stability is also relevant - researchers have shown that the half life for ribose destruction (key RNA ingredient - the "R") would be only a bit more than an hour in warmer waters. All chemical reactions cited by origin researchers which synthesize ribose, produce it only in racemic (random right and left hand) mixtures. However, left-handed ribose interferes with RNA synthesis. How can racemic mixtures be sorted in a fully natural environment?  Another major issue is the plausibility of a self-replicating RNA. In the decade since theory gained general acceptance, the search has been on in a number of labs to discover and  demonstrate a self-replicating RNA structure (since this is the core concept of the theory).	Existing cell RNA should provide good clues to the evolutionary history of self-reproductive RNA systems if they ever existed. Yet, in spite of the use of high-tech engineering, computer and laboratory methods (none of which were available on the early earth), no self-reproductive RNA system has yet been found. This failure has certainly not helped in promotion of the theory - although it is rarely mentioned by its proponents, as some still hope it may yet be found. Several researchers critical of the theory have pointed out that the catalytic potential of RNA is insufficient to accomplish full self-reproduction, so that in their opinion, a self-reproductive RNA is simply not possible. In all living cellular systems, proteins assist in completing the necessary reactions. Some researchers have suggested that various minerals such as clays could play a significant role in helping to catalyze various reactions, perhaps even helping to form the original RNA, however actual lab research has shown minerals provide little help, and any benefits occur only in a few reactions, certainly nothing like the hopeful statements found in some textbooks. The research to date has been unsuccessful enough that a number of researchers are starting to propose other possibilities - moving toward simpler precursors that might have evolved to become RNA (the Pre-RNA world). One suggested possibility is called peptide nucleic acid (PNA) but it has yet to be demonstrated as a more likely precursor than RNA - it suffers the same problems of plausibility, self-reproduction, etc. as RNA, with the added question of how it could evolve to become a self-reproductive RNA.  As yet, little concrete supportive evidence has been gathered in favor of the RNA world theory in spite of some considerable work and its status as "near dogma" in this field.

Continue on to Part 5: The  Staggering Complexity of Life's Simplest Forms
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