Phases of Mitosis.Mitosis is a process of continuous cell division in eukaryotic cells, where a cell gives rise to two other identical cells with the same number of chromosomes because before mitotic division the genetic material of the cell (in the chromosomes) is duplicated.
Phases of Mitosis
Mitosis has four main phases: Prophase, Metaphase, Anaphase and Telophase.
The main functions of mitosis are the formation of gametes in plants, embryonic development through divisions of the zygote, growth, tissue renewal and healing.
Mitosis occurs in somatic cells , that is, in most cells in our body and is an important process for cell regeneration, growth and development of multicellular organisms and asexual reproduction of unicellular organisms.
In addition to mitosis, there is another process of cell division called meiosis. The main difference between these two mechanisms is that mitosis is an equational process , which generates two genetically identical cells, while in meiosis the process is reductional, as the four cells that originate have half the number of chromosomes of the parent cell.
Phases of Mitosis
The cell cycle corresponds to the period of life of a cell in which several changes occur. The period in which the cell is carrying out its metabolic activities and performing its functions represents most of the cycle and is called interphase.
At a given moment, the cells start preparing for cell division, with cell growth and DNA replication, so that through mitosis the daughter cells originate.
Stage 1: Prophase
Prophase is the longest phase of mitosis. There are changes in the cell nucleus and cytoplasm.
Initially, there is a change in the nucleus due to the increase in nuclear volume. This is because the cytoplasm gives up water to the nucleus. This fact causes the cytoplasm to become denser.
At the beginning of prophase, each chromosome is made up of two strands called chromatids, held together at the centromere. As prophase progresses, the chromosomes become shorter and thicker. It’s chromosomal spiralization.
While the chromosomes are condensing, the nucleolus begins to become less conspicuous, disappearing towards the end of prophase.
The disappearance of the nucleolus is related to the fact that the synthesis of RNA in the chromosomes ceases. Since the nucleolus is a site of intense rRNA synthesis, with the condensation of the chromosomes this synthesis ceases and the nucleolus disappears.
The modification in the cytoplasm is verified in the duplication of the centrioles. After duplicating, they migrate towards the poles of the cell. After reaching the poles, they are surrounded by fibers that constitute the aster. Between the separating centrioles, the fibers of the mitotic spindle appear.
There are two types of fibers: continuous fibers, which go from centrioles to centrioles, and chromosomal or kinetochoric fibers, which only appear in prometaphase.
prometaphase
Prometaphase begins with the breakdown of the nuclear envelope . When this happens, the chromosomes fall into the cytoplasm and head to the equatorial region of the cell, where the spindle fibers will attach through the centromere.
Stage 2: Metaphase
At metaphase , the chromosomes attached to the spindle by the centromere meet in the equatorial plane of the cell forming the so-called metaphase or equatorial plate .
In this phase of cell division, chromosomes remain stationary for a long time. Meanwhile, in the cytoplasm, there is intense movement of particles and organelles, which are evenly directed to opposite poles of the cell.
Step 3: Anaphase
Anaphase begins when the centromere of each duplicated chromosome splits lengthwise, separating the sister chromatids .
As soon as they separate, the chromatids are called sister chromosomes, and are pulled to opposite poles of the cell, guided by spindle fibers.
When the sister chromosomes reach the poles of the cell, anaphase ends. Thus, each pole receives the same chromosomal material, since each sister chromosome has the same genetic information.
: TelophaseStep 4
Telophase is the last phase of mitosis. In it, the reverse of what happened in prophase and the beginning of prometaphase occurs.
The nucleus reorganizes itself, the chromosomes decondense, the kinetochore and the cimetochore fibers disappear and the nucleolus reorganizes itself (with the decondensation of the chromosomes, RNA synthesis begins and, consequently, the nucleus reappears).
At the end of telophase, the two nuclei acquire the same appearance as an interphase nucleus.
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