[The origin of the eukaryotic cell. II. A critical analysis of the symbiotic (exogenous) concept]

The exogenous (symbiotic) conception of the eukaryotic cell origin is unable to explain satisfactory the structure of mitochondria and chloroplasts. Either of these organelles possess its genome that can be compared with the viral one rather than with the bacterial one, judging by the dimensions and quantity of coding genes. The mitochondria resemble a little prokaryotes in the number of their proteins, chemical composition of their inner membrane and peculiarities of the protein-synthesizing apparatus. The primitive structure of mt DNA, the lesser quantity and greater unspecifity of the mitochondrial tRNA prove, additionally, the non-bacterial origin of this organelles. The deflexion of the genetic code from the universal one in the mitochondrial nucleoids also testify in favour of this point of view. The results of micropaleontological and paleobiochemical investigations evidence towards initial ability of the primary eukaryotes (primary protists) to photosynthesis. In this case, they did not need to acquire plastids from outside by symbiotic way. The autogenous origin of the flagellum of the primary protists was reported earlier (Seravin, 1985). The accumulated data permit us to consider that the cell organelles formed endogenously in the process of evolution of the cell.