The life cycle of a cell - the period from its birth to self-division or death

The life cycle of a cell is the period of existence of an elementary unit of a living from its appearance by division to its own division or death. It includes all the regular changes that organelles undergo, performing their functions.

Depending on its organization and specialization, the cell’s life cycle can last as long as 30 minutes, and for 3 days. For example, when cells are split 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 living things that do not divide, that is, do not multiply, they fulfill their intended functions and die - for example, nerve, striated muscle fibers. The life cycle of the cell itself is usually divided into two periods: interphase, or growth period, and mitosis - the period of division. The interphase includes, respectively, several phases:

1. G1 (postmitotic) - initial growth phase. At this stage, the assembly of mRNA, proteins and other components of the cell occurs.
2. S (synthetic) - DNA replication occurs, which leads to a doubling of genetic material. At the end of the phase, two identical double DNA helices are formed. Each of the chains of deoxyribonucleic acid contains one old spiral, and the second a new one, which was formed by the principle of complementarity.
3. G2 (premitotic) - there is a process of repair, which includes the correction of errors made in the synthesis of DNA in the previous phase. Nutrients, 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 new generation daughter cells. Mitosis is the main type of division of somatic (not taking part in sexual reproduction) elementary units of nuclear organisms.

The life cycle of the cell is essential for the body, ensuring the safety of the number and shape of the chromosomes characteristic of each species (karyotype), therefore it is important that all periods of division pass without any violations. Mitosis consists of 4 consecutive phases:

1. Prophase. During this period, division occurs in the cell and diverges to the poles of centrioles, which are interconnected by a spindle of division. By the end of this period, the nucleoli decay, the chromosomes thicken and shorten, i.e. going on
   
   their condensation.
2. Metaphase. Nucleoprotein structures line up at the equator of the cell, a metaphase plate is formed. Primary constriction of chromosomes occurs. Then each of them is divided into 2 chromatids.
3. Anaphase. In this phase, the resulting daughter chromosomes move to different poles, where they thin and unwind.
4. Telophase. The nucleolus and nucleus are restored, and cytoplasm is divided.

Thus, the cell cycle is the time of life from birth to the death of an elementary unit of the living.