Preparation of cells for division was called interphase. It consists of three periods.
The presynthetic period (G1) is the longest part of the interphase. It can continue in various types of cells from 2-3 hours to several days. This period immediately follows the previous division, during which the cell grows, accumulating energy and substances for the subsequent doubling of DNA.
The synthetic period (S), which usually lasts 6–10 hours, includes the doubling of DNA, the synthesis of proteins necessary for chromosome formation, and the increase in the amount of RNA. By the end of this period, each chromosome already consists of two identical chromatids, connected to each other in the region of the centromere. In the same period, centrioles double.
The postsynthetic period (G2) occurs after chromosome doubling. It lasts 2–5 hours; during this time, energy is accumulated for the upcoming mitosis and microtubule proteins are synthesized, which subsequently form the division spindle. Now the cell can proceed to mitosis.
Before proceeding to the description of cell division methods, we consider the process of DNA doubling, as a result of which sister chromatids are formed in the synthetic period.
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