Mitosis division

Mitosis division

1. Shri Shankaracharya Mahavidyalaya , Junwani , Bhilai Dr. Sonia Bajaj (Head of Department) Mitosis

2. Division phase Division phase or M-phase or mitotic phase lasts for only about an hour in the 24 hour duration of cell cycle of a human cell. I t is the phase of shortest time in cell cycle. The M-phase start with nuclear division, corresponding to the separation of daughter chromosome ( karyokinesis ) and usually ends with division of cytoplasm (cytokinesis).   Mitosis is divided into the following four stages – Prophase Metaphase Anaphase Telophase Division of nucleus in mitosis and meiosis is indirect.

3. Prophase (longest stage) Prophase which is the first stage of mitosis follows the S and G 2 phase of interphase. Metabolism of cell decrease, cytoplasm become viscous, refractive and pale. Chromosome are seen to be longitudinally consisting of two chromatid attached together at the centromere. At primary stage of nucleus and chromatin network become more conspicuous and visible. Chromosome become clearly visible inside nucleus. Chromosome becomes shorter and thicker In late prophase, nuclear membrane and nucleolus disappears.

4. 2. Metaphase This then, is the stage at which morphology of chromosome is most easily studied. Nuclear membrane and nucleolus disappear completely. Chromosome become shortest and thickest at this stage and so this is the best phase to study chromosome. Spindle fibres are formed from poles to centre which are made of the of microtubules) With the help of this spindle fibres , chromosome are arranged on the equatorials plate. Spindle fibre attach to kinetochores of chromosome. Spindle fibre are composed of 97% tubulin protein and 3% RNA. Centromere lies at equator and arms remain directed towards poles. Spindle fibre are two types- 1. Discontinuous spindle fibre - discontinuous spindle fibre these are joint with centromere of chromosome. 2. Continuous spindle fibre - continuous spindle fibres these are continuous from one pole to other and not joint with centromere of chromosome.

5. 3. Anaphase (shortest stage) It is shortest duration. Chromosome are thickest during this phase. Each chromosome splits by splitting of centromere , and both the chromatid of each chromosome separate from each other. Chromatid thus separated are called daughter chromosome. Daughter chromosome move towards opposite poles due to repulsion and contraction of spindle fibres . Approximately 30 ATP are required to carry a chromosome to pole. Chromosome reach at poles in late anaphase. Chromosome split and chromatid separate. Chromosome with one chromatid move to opposite poles. Chromosomal spindle fibres pull the chromosome towards the poles and the chromosome appear- V shaped (metacentric), L shaped (sub metacentric), J shaped (acrocentric), I shaped (telocentric).

6. 4. Telophase (Reverse prophase) At the beginning of the final stage of mitosis. This is the last phase of mitosis. Daughter chromosome which two opposite poles. Nuclear membrane developed at each pole around chromosomal group. Nucleolus also reappear. In this way, nuclear division or karyokinasis is completed. Aster rays and spindle fibres are absorbed in cytoplasm. Nuclear envelope assembles around the chromosome clusters. .

7. Cytokinesis -After nuclear division, division of cytoplasm take place. It may happen by any of the following two method- By cell plate formation - It occur in plants. In such cases, cell plate is laid down. It is usually initiated in the Centre and move towards periphery.   By cell furrow formation - In animal, cell wall is lacking and outermost cell membrane is flexible. A circular construction appears at equator and its converges on all sides finally separating the two daughters cells. Cytokinesis start in late anaphase. In animal center of cytokinesis occurs by the constriction and furrow formation.

8. Significance of mitosis Development of an organism occur by mitosis. Every organism starts in the life from a single cell witch zygote. Repeated mitosis in zygote leads to the formation of whole body. The growth of multicellular organism is due to mitosis . Cell growth result is disturbing and ratio between the nucleus and the cytoplasm .it therefore become essential for the cell to divide to restore and nucleo - cytoplasmic ratio. A very significant contribution of mitosis in cell repair. The cell of the upper layer of the epidermis ,cell of the living of the gut, and blood cell are being constantly replaced . M itotic division in the marriage thematic tissue the apical and later cambium result in the continuous growth to plant throughout their life.