life cycle of cells - the period of the elementary unit of living on her own appearance before the division of division or death.It includes all the natural changes that undergo organelles carrying out its functions.
Depending on its organization and specialization, the life cycle of a cell can last at 30 minutes and 3 days.For example, by crushing cells echinoderms the life cycle of 30 minutes, and human intestinal epidermis - 12 hours.There are some basic unit of the living that can not be divided, that is. E. Do not reproduce, they perform their intended function and die - for example, nerve, striated muscle fibers.The life cycle of the cell itself can be divided into two periods: interphase, or the period of growth, and mitosis - the period of division.Interphase includes, respectively, a number of phases:
- G1 (post-mitotic) - initial phase of growth.At this stage, the assembly of the mRNA, proteins and other cell components.
- S (synthetic) - DNA replication occurs, which leads to a doubling of genetic material.At the end of phase two of the same form DNA double helix.Each of the chains of deoxyribonucleic acid contains a single spiral old, and the second - a new one, which was formed on the principle of complementarity.
- G2 (premitoticheskuyu) - the process of reparation, which includes correction of errors made in DNA synthesis in the previous phase.Accumulating nutrients, energy, continue to synthesize proteins and RNA.
key element of reproduction is the mitotic cell cycle, or proliferative, which begins immediately after the G2.It is a set of processes that occur in the elementary structural unit of living from one division to another and end with the formation of a new generation of daughter cells.Mitosis is the main type of division of somatic (not participating in sexual reproduction) elementary units of nuclear organisms.
life cycle of cells is essential for the body, ensuring the safety of the number and shape of chromosomes characteristic of each species (karyotype), so it is important that all periods of the division took place without any disturbances.Mitosis consists of 4 successive phases:
- Prophase.During this period, the cell is dividing and divergence of centrioles to the poles, which are interconnected division spindle.By the end of the period split nucleoli, chromosomes thicken and shorten, ieIt is their condensation.
- Metaphase.Nucleoprotein structure at the equator of the cell lining formed metaphase plate.It is the primary constriction of the chromosomes.Then, each of them divided into 2 chromatids.
- Anaphase.In this phase obrazovashiesya daughter chromosomes move to different poles, where they are flat out and unwind.
- Telophase.Restores the nucleolus and the core, is the division of the cytoplasm.
Thus, the cell cycle - the time of life from birth to death of the elementary unit of living.
