The life cycle of a cell is the period of existence of an elementary unit of the living from its appearance by division to its own division or death. It includes all the regular changes that organelles undergo while performing their functions.
Depending on its organization and specialization, the life cycle of a cell can last either 30 minutes or 3 days. For example, during cell fragmentation in echinoderms, the life cycle time is 30 minutes, and the intestinal epidermis in humans is from 12 hours. There are also such elementary units of the living that do not divide, i.e., do not multiply, they perform their intended functions and die - for example, nerve, striated muscle fibers. The cell life cycle itself is usually divided into two periods: interphase, or the period of growth, and mitosis, the period of division. Interphase includes, respectively, several phases:
- G1 (post-mitotic) - phase of initial growth. At this stage, mRNA, proteins and other components of the cell are assembled.
- S (synthetic) - DNA replication occurs, which leads to a doubling of the genetic material. At the endphase, two identical DNA double helixes are formed. Each of the chains of deoxyribonucleic acid contains one old helix, and the second - a new one, which was formed according to the principle of complementarity.
- G2 (premitotic) - the repair process is underway, which includes the correction of errors made during DNA synthesis in the previous phase. Nutrients and energy accumulate, proteins and RNA continue to be synthesized.
The key link in reproduction is the mitotic cycle of the cell, or proliferative, which immediately begins after G2. It is a set of processes that occur in the elementary structural unit of the living from one division to another and end with the formation of daughter cells of a new generation. Mitosis is the main type of division of somatic (not participating in sexual reproduction) elementary units of nuclear organisms.
The life cycle of a cell is essential for the body, ensuring the preservation of the number and shape of chromosomes characteristic of each species (karyotype), so it is important that all periods of division pass without any disturbance. Mitosis consists of 4 successive phases:
- Prophase. During this period, the cell divides and diverges to the poles of the centrioles, which are interconnected by the division spindle. By the end of this period, the nucleoli disintegrate, the chromosomes thicken and shorten, i.e. happening
- Metaphase. Nucleoprotein structures line up along the equator of the cell, a metaphase plate is formed. There is a primary constriction of chromosomes. Then each of them divides into 2 chromatids.
- Anaphase. In this phase, the resulting daughter chromosomes move to different poles, where they thin out and unwind.
- Telophase. The nucleolus and nucleus are restored, and the cytoplasm divides.
their condensation.
Thus, the cell cycle is the time of life from birth to death of an elementary unit of life.
