Cellular Biology

Mitosis



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DEFINITION

All living organisms in this world are made up of cells. Cell (cellulae) is the basic unit of life. All cells undergoes numerous processes including cell division. Cell division can be divided into two types: mitosis and meiosis. All types of cells except gametes undergo mitosis.

Mitosis is the cell division process that produces 2 daughter cells with the same chromosomal number and DNA contents as the original cell. Mitosis is just a part of a cell cycle. Usually, a mitosis process last about one hour. Mitosis consists of 5 subphases:

a) Prophase

b) Metaphase

c) Prometaphase

d) Anaphase

e) Telophase

ROLES OF MITOSIS

There are many roles of mitosis. Among them are:

a) Enables the unicellular organisms such as Amoeba to form duplicate offspring.

b) Enables sexually reproducing organisms to develop from a single cell the fertilized egg or zygote.

c) Enables the growth of organisms.

d) Renewal and repair, replacing cells that die from normal wear and tear or accidents. For example, dividing cells in your bone marrow continuously make new blood cells.

PHASES OF MITOSIS

1. PROPHASE

During prophase, changes occur both in nucleus and cytoplasm. In the nucleus, the nuclear envelope and mucleous begin to disappear. The chromatin fibers become more tightly coiled condensing into thick chromosomes which are visible in the light microscope as a ball of thread. Each duplicated chromosomes appears as two identical sister chromatids joined together by centromere. In the cytoplasm, two centrioles migrate towards the opposite poles. The mitotic spindle made of microtubules extending from the centrioles begins to form.

2. PROMETAPHASE

During prometaphase, the nuclear envelope in nucleus fragments. The microtubules of the spindle can now invade the nuclear area and interact with the chromosomes that have become thicker and more condensed. Bundles of microtubules extend from each pole towards the center of the cell. Now, each of the two sister chromatids have a specialized structure called a kinetochore located at the centromere region. Some of the microtubules attached at the kinetochores causing the chromosomes to begin jerky movements. Nonkinetochore microtubules interact with those from the opposite pole of the cell.

3. METAPHASE

The microtubules reached the opposite poles. The chromosomes convene on an imaginary plane that is equidistant between the spindle's two poles. This imaginary plane is called the equatorial plate or metaphase plate. The centromeres of the chromosomes are all on the equatorial plate. For each chromosome, the kinetochores of the sister chromatids are attached to microtubules coming from opposite poles of the cell. The entire apparatus of microtubules is called the spindle because of its shape.

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4. ANAPHASE

The anaphase begins when the paired centromeres of each chromosome suddenly separate, finally liberating the sister chromatids from each other. The once joined sisters, each now considered a fully fledged chromosome, begin moving toward opposite poles of the cell as their kinotochore microtubules shorten. Because these microtubules are attached at the centromere, the chromosome move centromere first . At the same time, the poles of the cell move far apart, as the nonkinetochore microtubules lengthen. By the end of anaphase, the two poles have equivalent and complete collections of chromosomes.

5. TELOPHASE

At telophase, the non kinetochore microtubules elongate the cell still more, and the daughter nuclei form at the two poles of the cell. Nuclear envelope arises from the fragments of the parent cell's nuclear envelope and other portions of the endomembrane system. The chromosomes become less coiled and becomes thinner. Nuclear membrane reformed around the chromosome at each pole. Mitosis, the division one nucleus into two genetically identical nuclei, is now complete. The division of cytoplasm, cytokinesis is usually well under way by this time, so two daughter cells appear shortly after the end of mitosis.

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