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Figure 3–6. Influence of the nucleus on the formation of umbel in Acetabularia mediterranea (med.) and Acetabularia crenulata (cren.) (After Swanson and Webster, 1980). The nucleus of donor cell determines the shape of umbel (a, b). If unite rhisoids of the two species, the umbel combines the distinctive features of loose rays of A. crenulata and round shape of A. mediterranea (c).
In case of successful transplantation the restoration processes in the
cells run even faster, sometimes for minutes. This confirms the concept of
first-rate role of this organelle in the life processes of cell as a whole.
The cell nucleus possesses a complex structural organization and
chemical composition, which are a subject of special literature on this
question. They are closely related with the functions performed by it as a
basic genetic and regulating organelle of the cell.
The process of evolution has also shown its great creative capacity on
the structural organization of the nucleus. While in prokaryotic cells the
nucleoid is “freely” located in the cytoplasm, in eukaryotic cells the nucleus
is separated from it through a double nuclear membrane. The latter isolates
the basic genetic processes in the nucleus, related with DNA replication
and transcription and mRNA synthesis, from the processes of protein
synthesis realizing in the cytoplasm (see Fig. 2–35). Such spatial
separation of these processes is a qualitatively new stage in evolutionary
development of the cell. Besides, eukaryotic DNA, in contrast to
prokaryotic, is much more closely connected with histone and non-histone
proteins, that ensure its compact package and participate in gene
expression as well as in controlling the metabolic processes in cells. The
chromatin arises and the division spindle is formed.