Indirect division, also called karyokinesis or mitosis (Greek: mitos —
threads), is a basic mode of division in eukaryotic cells, which have well-
formed nucleus, surrounded by a nuclear envelope. It is observed by a lot of
investigators — R. Remak, L. Auerbach, A. Schneider, O. Bütschli, I.
Chistyakov, E. Strasburger, etc., but it wins recognition with the works of
Flemming (1882 a, b) and van Beneden (1883 a, b) mentioned in Section 3. 2.
Mitosis is realized in two mutually connected stages: a) division of the
nucleus (karyokinesis); b) division of the cell (cytokinesis). This is
represented in Figure 3–8.
In order to be divided, the cell passes its life way, called cell cycle or
generation time (Fig. 3–9). Before to start the division it remains in the
so-called interphase, which spans the period between two consecutive
mitoses. For a long interphase was considered “period of repose”. It proved
that “the repose” is not intrinsic to the life. During the interphase there run
intensive preparatory processes. To reach the division of nucleus (phase M —
mitosis), it is necessary to synthesize DNA (phase S — synthesis). The period
between phase M and the beginning of DNA synthesis is denoted as phase
G₁, and the period after the termination of DNA synthesis and phase M — as
G₂. Actually, interphase includes the phases G₁, S and G₂. Its duration varies
in broad limits for the different kinds of cells (from hours to days, months and
more). Then the division begins. In some lower eukaryotic organisms phase
G₁ is absent and after the end of division the cells enter in phase S
immediately.
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Figure 3–8. Scheme of mitotic division as a process. Mitosis is divided in five phases — prophase, prometaphase, metaphase, anaphase and telophase. After that cytokinesis occurs. This process is represented in Figure 3–10.
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Figure 3-9. Scheme of cell cycle.