Interphase(redirected from karyostasis)
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interkinesis, the stage in the life cycle of a cell between two successive mitotic divisions.
A distinction is usually made between the heterosynthetic interphase, when the cell grows, is differentiated, and performs its natural functions, and the autosynthetic interphase, during which the cell prepares for the next division. Depending on the intensity of synthesis of desoxyribonucleic acid (DNA), the autosynthetic interphase is divided, in turn, into three periods: G1– presynthetic, or postmitotic; S—synthetic; and G2—premitotic, or postsynthetic. During the G1 period the energy resources needed for cell division accumulate, ribonucleic acid (RNA) is synthesized, and preparation is made for the replication of DNA molecules. The cell mass enlarges because of the protein synthesized at this time, and several enzymes needed for DNA synthesis during the subsequent period are formed. DNA is synthesized during the S period—that is, its molecules are replicated. DNA synthesis is completed during the G2 period and the synthesis of RNA and proteins intensifies, apparently in order to construct the mitotic apparatus.
In the cells of an adult organism the interphase takes 10 to 30 hours or more, but in rapidly dividing cells it lasts just several minutes (for example, 14 min. in sea urchin eggs at the two-to-four-blastomere stage).
Some investigators distinguish in the interphase a “zero period” (Go) that precedes the G1 period. The G0 is most clearly manifested in cells that as a rule do not divide in the adult organism (under the influence of various factors they may enter the G1 period, pass through the S and G2 periods, and enter into mitosis proper). The boundary between all the periods of the interphase or between mitosis and the interphase is not sharp. Some investigators believe that the S and G2 periods should be regarded as the beginning of mitosis (the preprophase, during which cell reproducton also begins), and not as part of the interphase.
REFERENCESMeziia, D. Mitoz i fiziologiia kletochnogo deleniia. Moscow, 1963.
Alov, I. A., A. I. Braude, and M. E. Aspiz. Osnovy funktsional’noi morfologii kletki, 2nd ed. Moscow, 1969.
M. E. ASPIZ