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Mitosis is the process of nuclear division in a living cell by which the chromosomes are exactly replicated, the two parts being separated are given to the daughter nuclei. In this process the two daughter cells receive chromosomes that are alike in composition and equal in the number of chromosomes as the parent cell. Mitosis consists of four main stages. Mitotic division occurs in somatic (body) cells. The stages are prophase, metaphase, anaphase, and telophase.
In interphase the cell seems to be inactive for most of the time. Really the cell is undergoing normal cell processes, and all metabolic activities. Towards the end interphase the cell undergoes preparations for cell division, yet sometimes in this stage the chromosome duplicate. Interphase consists of three stages: Growth one, S phase (DNA synthesis), Growth two.
In growth one a newly formed cell synthesizes materials for cell growth. In S or DNA synthesis, the DNA is replicated. At this stage DNA consists of long thin strands called chromatin. As each strand is duplicated it is attached to its duplicate by a structure called a centromere. In the last stage known as Growth two, special enzymes correct any errors in the newly synthesized DNA. Prophase the first part of mitosis is the stage where the chromosomes begin to condense into visible threads that become progressively thicker and shorter.
The centrioles have already duplicated before the division process begins. The centrioles now begin to move apart. As they do long fibers appear in the cell, these fibers are called microtubules (spindle fibers). The centrioles move to opposite sides of the cell, at the same time, the network of fibers extends across the cell between the two poles, forming a spindle.
The microtubules attach to the chromosomes at spots called kinetochores. Towards the end of prophase, the nuclear envelope dissolves. The next phase is called metaphase. In metaphase the chromatids move toward the middle of the spindle called the equator. The chromatids are still joined but are lined up on opposite sides of the equator. Anaphase is the phase where the chromosomes are separated.
They are pulled apart by the spindle fibers, in opposite direction of the poles of the dividing cell. The mechanisms that control chromosome separation clearly involve the interactions between microtubules and components in and near the kinetchore. The last phase of mitosis is telophase. The chromosomes move and gather around close to the spindle pole region, and the spindle midline starts to clear. The cytoplasm is divided between the eventually new cells. In the middle of the spindle region a thin line of vesicles starts to form.
In plants the cell wall is formed. Then cytokinesis starts, the line forms the new cell membrane. Now two totally functional cells have been formed. Both cells are genetically identical.
Mitosis is happening all the time, in fact it happens 25 million times a second in the human body. Mitosis brings meaning to the cell theory, "All cells are the units of structure and function in living organisms / And all new cells come from cells that already exist. " Mitosis is vital for growth, repair and replacement of damaged or worn out cells; and also for asexual reproduction. Bibliography:
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