The unified conception of the origin of eukaryotic cells has been proposed. In the author's opinion, evolutionary
transformation of prokaryotic cell into eukaryotic cell took place 3.3-1.4 billion years ago and involved the next four stages: 1) the
appearance of intracellular membranes due to prokaryotic cell plasmalemma invaginating into its cytoplasm; 2) the cell nucleus formation
by the double sheet of intracellular membrane surrounding and sequestrating genetic material of the cell; 3) the appearance of
cytoskeleton in parallel with mitotic spindle formation and gradual transition from prokaryotic way of cell division to mitosis; 4) the
establishment of symbiosis between the evolving nucleated cell and prokaryotic microorganicsms that subsequently transform into
mitochondria and chloroplasts. Apoptosis of cells of the present day multicellular eukaryotic organisms is supposed to be an evolutionary
altered response of mitochondrian predecessors to the influence of factors, which are able to damage eukaryotic host cell. The initial
biological significance of this reaction pertained to attempts of endosymbionts to leave the host cell as soon as possible, if the
probability of its irreversible injury was very high, and by this to escape from their death. It is possible that numerous proteins,
known as sensors or transducers of proapoptotic signals in Bcl-2-p53-dependent apoptotic pathway, were initially encoded by
mitochondria! genome, whereas antiapoptotic factors and also components of receptor-mediated and granzyme  perform dependent apoptotic
pathways have cellular origin.
Key words: eukaryotic cell, prokaryotic cell, evolution, symbiosis, apoptosis
