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  Phases of Cell Cycle of Mitosis, Biology tutorial

Introduction:

Mitosis is a type of eukaryotic cell division which produces or generates two daughter cells having the similar genetic component as the parent cell. Chromosomes replicated throughout the S phase are classified in such a manner as to make sure that each and every daughter cell obtains a copy of each chromosome. In actively dividing animal cells, the entire procedure takes around one hour.

The replicated chromosomes are joined to a 'mitotic apparatus' which aligns them and then separates the sister chromatids to generate an even partitioning of the genetic material. This separation of the genetic material in the mitotic nuclear division (or karyokinesis) is followed by a separation of the cell cytoplasm in a cellular division (or cytokinesis) to generate two daughter cells.

In certain single-celled organisms mitosis builds up the foundation of asexual reproduction. In diploid multicellular organisms sexual reproduction comprises the fusion of two haploid gametes to generate a diploid zygote. Mitotic divisions of the zygote and daughter cells are then accountable for the later growth and development of the organism. In adult organism, mitosis plays a function in cell replacement, wound healing and tumor formation.

Mitosis, however a continuous process, is usually classified into five phases: Prophase, Prometaphase, Metaphase, Anaphase and Telophase.

Prophase:

Prophase engages over half of mitosis. The nuclear membrane splits to form a number of small vesicles and the nucleolus disintegrates. A structure termed as the centrosome duplicates itself to make two daughter centrosomes which migrate to opposite ends of the cell. The centrosomes organize the production of microtubules which make the spindle fibers which comprise the mitotic spindle. The chromosomes condense to the compact structures. Each and every replicated chromosome can now be seen to comprise of two similar chromatids (or sister chromatids) held altogether through a structure termed as the centromere.

Prometaphase:

The chromosomes, led by their centromeres, transfer to the equatorial plane in the midline of cell at right-angles to the axis made by the centrosomes. This area of the mitotic spindle is termed as the metaphase plate. The spindle fibers join to a structure related with the centromere of each chromosome termed as a kinetochore. Individual spindle fibers join to a kinetochore structure on each and every side of the centromere. The chromosomes carry on condensing.

Metaphase:

The chromosomes line up themselves all along the metaphase plate of the spindle apparatus.

Anaphase:

It is the shortest phase of mitosis. The centromeres split or divide, and the sister chromatids of each and every chromosome are pulled apart or 'disjoin' and move to the opposite ends of the cell, pulled through spindle fibers joined to the kinetochore areas. The separated sister chromatids are now termed to as daughter chromosomes. (It is the basically the alignment and separation in metaphase and anaphase which is significant in making sure that each and every daughter cell gets a copy of each and every chromosome.)

Telophase:

It is the final phase of mitosis and a reversal of many of the procedures observed throughout prophase. The nuclear membrane reforms about the chromosomes grouped at either pole of the cell, the chromosomes uncoil and become diffuse and the spindle fibers vanish.

Cytokinesis:

The final cellular division to make two new cells. In plants a cell plate forms all along the line of the metaphase plate and in animals there is a constriction of the cytoplasm. The cell then enters Interphase, that is, the interval between the mitotic divisions.

Significance of Mitosis:

1) It is an equational division via which similar daughter cells are produced having the similar amount and kind of genetic constitution as that of the parent cell.

2)  It is basically responsible for growth and development of the multi-cellular organisms from a single-celled zygote.

3) The number of chromosomes remains similar in all the cells generated by this division. Therefore, the daughter cells retain similar features as those of the parent cell.

4) It assists the cell in maintaining the correct size.

5) Mitosis assists in restoring wear and tear in the body tissues, substitution of damaged or lost part, healing of wounds and renewal of detached parts (as in tail of lizards).

6) This is a process of multiplication in the unicellular organisms.

7) When mitosis remains unchecked, it might outcome in uncontrolled growth of cells leading to tumor or cancer.

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