Origin of Life in the Ocean: Direct Derivation of Mitochondria from Primitive Organisms Based on Complete Genomes

Abstract

The origin of life has long been of interest to humans. However, despite the continuous increase in new data regarding complete genomes, the “origin of life” is still unclear. To evaluate this subject, the normalization of genome figures such as nucleotide or amino acid contents, which were predicted from the complete genome, was carried out, because this process excludes experimental errors and is independent of genome size and type (reviewed in). We can speculate about past and future evolutionary phenomena based on the rules that govern the evolution of present day organisms. Animals were classified into two groups; aquatic and terrestrial, based on nucleotide contents, GC skews and the ratio of methionine to valine predicted from complete mitochondrial genomes. This classification was linked to ammonia (which is fatally toxic to organisms), urea and uric acid excretion. The cytosine contents of primate and bird complete mitochondrial genomes are the highest among organisms examined, while that of the aquatic single-celled choanoflagellate (Monosiga brevicollis) are the lowest. Thus, the former two groups are ranked most highly evolved organisms, because more highly evolved organisms seem to have greater levels of cytosine. In non-animal mitochondrial genomes, the cytosine content of Fungi (Smittium culisetae) is the lowest, while that of land plants is the highest. As the cytosine contents of M. brevicollis and S. culisetae mitochondria are close to the closing point of all extended nucleotide content regression lines obtained from mitochondrial, chloroplast and chromosomal genomes, we conclude that the mitochondrial ancestor might be derived directly from primitive organisms, and that all organisms and cellular organelles might be derived from the single origin of life. Keywords: Amino acid composition, cellular organelles, chargaff’s parity rules, eukaryotes, evolution, genome, normalization, nucleotide content, origin of life, prokaryotes.