Genetic Code

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In this chapter, the genetic code seems to be a universal code. The universal code has a specific arrangement of the codons that is definitely not random. There are at least three major concepts of the origin and the evolution of the universal genetic code: Firstly, there is the stereochemical theory stating that the assignments of codons are determined by the physicochemical affinity of the amino acids and the cognate codons (synonymously referred to as anticodons); secondly, the co-evolution theory stating that the structure of the code structure coevolved with the biosynthesis process of amino acids; and thirdly, the error minimization theory stating that there is a selection pressure minimizing the negative effects of point mutations and errors in translation were the main factor of code development. These theories are not contradictory and are also in line with the frozen accident hypothesis, such as the idea that the standard code may not have any special properties, but is simply determined by the fact that all existing life forms have a common ancestor, whereby later alterations to the code are generally excluded by the detrimental effect of codon reallocation. The mathematical examination of the structure and potential evolutionary trajectories of the code reveals that the code is highly resistant to translation errors, although there are numerous more resistant codes, suggesting that the standard code could emerge from a random code through a short sequence of rearrangements of series of codons. A large proportion of the evolution leading to the standard code seems to be a mixture of a frozen collision with a selection for error minimization, even though it cannot be excluded that the code co-evolves along with metabolic pathways due to weak affinities between amino acids and nucleotide triplets. These scenarios for code evolution, nonetheless, are founded on formal patterns with uncertain relevance to real primordial evolution. A true comprehension of code origins and developments is probably only possible in connection with a plausible script for the development of the coding scheme and the translation tool itself.