Wednesday, August 22, 2012

Mitosis - Cell Division

We all are aware of reproduction process in humans and in the animal kingdom. Have you ever thought about how reproduction takes place in the plant kingdom and in other eukaryotic organisms?
Plants and other eukaryotic cells do reproduce by separating the duplicated chromosomes and this process is known as mitosis. In this topic let's learn about mitosis and its various stages.
The basic mechanism of mitosis was described in early 1880s. The term mitosis was first coined by the scientist named "Fleming" in the year 1882. He studied and observed mitosis both in vivo and in stained preparation to study the process of cell division in unicellular animals.
Mitosis is generally defined as a type of cell division which occurs to form daughter cells, with same number of chromosomes as that of parental cells. This process is seen in all vegetative cells. In case of plants, mitosis is observed in all roots and shoot tip. In case of eukaryotic animals, mitosis is observed in organs related to the production of blood cells, skin cells, wound healing regions, etc.
Mitosis is divided in to six stages.
A cell during this stage of mitosis shows a clearly defined nuclear envelope, nucleolus and chromatin. We can also see the increased size of nucleolus. This phase is called as a resting period as division of cytoplasm and nucleolus does not take place. It is the longest phase of cell cycle which requires one to two days for completion.
· PROPHASE: (In Greek pro-first phase stage)
In this stage, the chromatin material of nucleus gradually condenses into distinct chromatin threads by using water. They gradually become thicker and shorter forming chromosomes. Nucleus and nuclear membrane gradually disappears at the end of prophase. It is the longest phase of cell cycle.
In this stage of mitosis the chromosomes move towards the equator of the cell, by attaching themselves to the spindle fibers with the help of their centromere. At the end of metaphase the centromere of each chromosomes divides to reach each chromatids to have its own centromere. These chromosomes further become shortened and thickened. The spindle fibers formed are of two types, namely chromosomal and polar spindle.
By the separation of chromatids, daughter chromosomes are formed towards the opposite pole of the cell along with the spindle fibers. At the end of anaphase each set of daughter chromosomes reach their respective pole. It is the shortest phase of mitosis as it lasts for few minutes.
· TELOPHASE: (In Greek telo-end phase stage)
In this stage of mitosis, two groups of chromosomes are formed, one at each pole. These chromosomes undergo uncoiling and become thread like structures. At the end of telophase nucleolus and nuclear membrane reappears and cytokinesis takes place by giving rise to new two cells.
In this stage of mitosis the cytoplasm of a single cell is divided in to two separate daughter cells.
Mitosis cell division is the process by which single cells reproduce themselves and multicellular organisms grow. This process is replication or multiplication. Mitosis is also called as an equatorial cell division and it takes place only in unicellular animals.

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