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

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

Depending on its organization and specialization, the life cycle of a cell can last as long as 30 minutes or 3 days. For example, when the cell is fragmented in echinoderms, the life cycle time is 30 minutes, and the human epidermis of the intestine is from 12 hours. There are also elementary units of the living that do not divide, that is, do not multiply, they perform their intended functions and perish - for example, nerve, striated muscle fibers. The life cycle of a cell is usually divided into two periods: interphase, or growth period, and mitosis - the period of division. Interphase includes, respectively, several phases:

1. G1 (postmitotic) - the phase of initial growth. At this stage, mRNA, proteins and other cell components are assembled.
2. S (synthetic) - DNA replication occurs, which leads to a doubling of the genetic material. At the end of the phase, two identical double helices of DNA are formed. Each of the strands of deoxyribonucleic acid contains one spiral old, and the second - a new one, which was formed by the principle of complementarity.
3. G2 (pre-tertiary) - a process of repair is underway, which includes the correction of errors made in the synthesis of DNA in the previous phase. Nutrients and energy accumulate, proteins and RNA continue to be synthesized.

The key link in the reproduction is the mitotic cycle of the cell, or proliferative, which begins immediately after G2. It is a collection 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 participating in sexual reproduction) elementary units of nuclear organisms.

The cell's life cycle is of great importance for the organism, ensuring the safety of the number and shape of chromosomes characteristic for each species (karyotype), so it is important that all periods of division pass without any disturbance. Mitosis consists of 4 consecutive phases:

1. Prophase. During this period, the cell divides and diverges to the poles of the centrioles, which are connected by a fission spindle. By the end of this period, the nucleoli break down, the chromosomes thicken and shorten; Occurs Their condensation.
2. Metaphase. Nucleoprotein structures are aligned along the equator of the cell, a metaphase plate is formed. There is a primary constriction of chromosomes. Then each of them is divided into 2 chromatids.
3. Anaphase. In this phase, the formed daughter chromosomes move to different poles, where they thin out and unwind.
4. The telophase. The nucleolus and nucleus are restored, the division of the cytoplasm occurs.

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