Introduction

Genetic information in the form of DNA base sequences or codon sequences is transformed into mRNA and then into amino acid sequence of proteins, according to the genetic code. But, double-stranded DNA, which carries genetic information, cannot be replicated without enzyme proteins, whereas proteins cannot be reproduced without genes. This dilemma made it difficult to account for the origin of life: this is the so-called chicken and egg relationship between genes and proteins in the life system.

The RNA world hypothesis on the origin of life is generally considered as the key to solve the “chicken and egg dilemma” concerning the evolution of genes and proteins as observed in the modern organisms. This hypothesis, however, contains several serious weak points, as followings. (i) Nucleotides would never be synthesized under pre-biotic conditions through a random combinatory process from simple chemical compounds such as water, carbon dioxide, methane, without proteineous enzymes. (ii) Existence of four hydroxyl groups on ribose also makes it difficult to synthesize RNA by joining nucleotides in the absence of enzyme catalysts. (iii) Self-replication of RNA must be practically impossible due to the following self-contradiction. RNA without any stable tertiary structure would be required to exhibit genetic function as a template, and, simultaneously, RNA would have to be folded into a stable tertiary structure to exhibit its catalytic function.

I have a counterproposal called [GADV]-protein world hypothesis, abbreviated as GADV hypothesis, in which I have suggested that life originated from a [GADV]-protein world, which comprised proteins composed of four amino acids: Gly [G], Ala [A], Asp [D], and Val [V]. A new concept “pseudo-replication” is crucial for the description of the emergence of life. The new hypothesis not only plausibly explains how life originated from the initial chaotic protein world, but also how genes, the genetic code, and proteins were originated and co-evolved.

 


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