The Non-Universality of the Genetic Code

(And Its Implications)

Original studies of the genetic code demonstrated that it was constant throughout the plant, protists, and animal kingdoms. It was taught (even in my college days) that the genetic code should be universal as predicted by the theory of evolution, since alterations of the genetic code would be lethal in those individuals which acquired genetic code mutations. Recently, many examples of variations in the genetic code have been discovered in many species of unrelated organisms. Although first shown in 1979 by Barrell et. al (1), subsequent studies have demonstrated that the genetic codes differs in diverse groups of unrelated animals, plants, and protists (2). There is no pattern of change in the code of related groups of organisms and none of the organisms which possess altered genetic code exhibit any form of evolutionary descent or common ancestry which might imply that the genetic code had evolved.

Introduction to the genetic code and protein translation:

The molecule depicted on this page (Figure 1) is transfer RNA (tRNA). This molecule is responsible for translating messenger RNA (mRNA) to protein. Amino acids (the building blocks of proteins) are bound to the top end of the molecule. The bottom of the molecule binds to specific mRNA sequences, which adds amino acids to form the protein. The bottom portion of the tRNA molecule provides specificity to the genetic code, since it binds to only one specific mRNA sequence. All organisms which differ from the universal genetic code do so through a single change in the bottom portion of the tRNA molecule. This single change causes the tRNA to bind to a completely different mRNA sequence (see Figure 2). Therefore, this change would cause one amino acid to be substituted by another amino acid. This kind of mutation would result in wholesale changes to all the proteins of an organism, which would alter protein function so that it would be lethal to 100% of these mutants.
 

Figure 2. Translation of same mRNA by (A), wild type and (B), tRNA mutant

Since evolution requires a process by which the genetic code would be altered, evolutionists propose that organisms that express a non-standard genetic code must be genetic mutants. The problem is that this single point mutation would result in an organism which could not survive. This is not just my opinion. Even proponents of evolution agree that 100% of these tRNA mutants would be unable to survive. Dr. T.H. Jukes (University of California, Berkeley) has stated, "Any mutational change in the code would be lethal, because it would produce widespread alterations in the amino acid sequences of proteins. Such changes would destroy protein function, and hence would be intolerable." What these scientists have really found to be "intolerable" is what these "mutations" disclose about the theory of evolution.

tRNA "Mutants" of the "Universal" Genetic Code

What kinds of changes would tRNA mutations result in? Table 1 describes a number of these tRNA mutants, including the kinds of organisms and the changes in amino acids coded for. One can see that many of these mutations substitute amino acids that alter the configuration of protein, which virtually guarantees that its function will be destroyed. It actually gets worse in other instances. In some of the genetic code mutants, former stop codons (which cause protein synthesis to halt when the protein reaches the proper size) now code for amino acids, which would result in longer proteins. Increasing the length of proteins would cause conformational changeswhich would result in inactivation of function. The most lethal of all these mutants would be the ones which changed from coding for arginine to coding for the stop sequence. This mutant would produce proteins with very short polypeptide chains, since protein synthesis would stop at every instance where arginine (AGR) was coded. Some proteins would not be made at all and virtually all other proteins would be non-functional.
 

The evidence is overwhelming and the problem an extremely profound one. This problem has been largely ignored by the scientific community and even the community of creationary scientists, despite its obvious implications. Those who have proposed evolutionary explanations have done so using mechanisms that are so improbable as to be statistically impossible. Here is their explanation:
 

We propose that the changes are typically preceded by loss of a codon from all coding sequences in an organism or organelle, often as a result of directional mutation pressure, accompanied by loss of the tRNA that translates the codon. The codon reappears later by conversion of another codon and emergence of a tRNA that translates the reappeared codon with a different assignment (2).

The Problem of Mechanism

Here is the essence of what evolutionists are proposing. They propose that every instance of a specific sequence (codon) in the DNA is mutated and replaced by anothe sequence. This requires replacement of 1-5% of the entire genetic sequence of an organism. Although this doesn't seem like a large amount of the genome, it is the specificity of replacement which makes this mechanism statistically impossible. In the case of vertebrates, this replacement would require millions of specific point mutations. There is no "directional mutation pressure" which would cause only one sequence to be replaced in an organism, even according to evolutionary theories. Evolution states that selection acts on the protein structure to improve its function. Since we are talking about all the proteins in an organism, there is no one selective pressure which would work to improve the function of all proteins simultaneously (especially by substituting only one specific amino acid for another).

The Problem of Descent

The existence of genetic code mutants in diverse groups of unrelated organisms presents a significant problem in evolutionary theory. Since all life must be related to their relatives, the genetics must also reflect this fact. These tRNA mutants present a glaring problem in terms of descent. One would expect that related organisms would exhibit some form of evolutionary tree in regard to the genetic code mutants. Instead, what we find are randomly isolated individual species of organisms which possess these genetic code mutations. If the mechanism for producing these mutations was evolution, we would expect to find whole families and orders of organisms with these kinds of mutations. Alternatively, we must accept that all of these mutations occurred relatively recently, such that there would be no record of descent. If this form of mutation could occur in organisms ranging from bacteria to fungi to vertebrates, it would have been expected to have happened in the past when these organisms first appeared.

Conclusions

In conclusion, there is no reasonable evolutionary mechanism by which tRNA point mutations can occur in such a diversity of organisms. Evolutionists must believe in a magical directional mutation pressure which replaces all of one specific codon sequence in a variety of unrelated species. In addition, they must believe that none of these species have evolved once this mutation occurred, since there is no evidence of descent. The alternative, that a Creator designed tRNA "mutants" to show us that He and not blind chance is responsible for life, is intolerable to those whose "faith" is evolution.

References
 

1. G. Barrell, A. T. Bankier, and J. Drouin. 1979. Nature [London] 282: 189-194.
2. Osawa S. Jukes TH. Watanabe K. Muto A. 1992. Microbiological Reviews 56 (1): 229-64.

Last updated 11/17/99