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Mitosis and Stages Of Mitosis with diagram

Mitosis and Stages Of Mitosis with diagram

This assignment about Mitosis and stages of mitosis is uploaded by Name Ummara Younis, Roll no CHEM 20-21

Assignment topic Mitosis and Stages Of Mitosis with diagram

Date 18 August 2021

MITOSIS Definition and Discovery

Mitosis is defined as a number of chromosomes remains constant in daughter cells just like the parent’s cell“.

Mitosis produces genetically identical cells. The division is also called somatic cell division or equational division or indirect division. Any cell of a living organism other than the reproductive cells is known as a somatic cell.

Mitosis was discovered by “Walther Fleming in 1882″.

Establishment :

Strasburger observed mitosis in plants.

▪Boveri and Fleming observed the same in animals.

Duration of Mitosis:

Dependent on the type of cell involved and its species, it takes 30 minutes to 3 hours. The various factors affecting the duration are types of the tissue, its location, temperature and species.

Occurrence :

• Plant meristematic (shoot and tip) tissues.

• animal skin

• bone marrow

EVENTS OF MITOSIS :

Major steps of mitosis are similar in plants as well as in animals. Mitosis is a very important type of cell division for all organisms. Mitosis is a continuous process but conventionally it is divided into two phases.

1: karyokinesis

It involves the division of the nucleus.

2: Cytokinesis

It refers to the division of the whole cell.

KARYOKINESIS

●Partition of Centriole :

At the start of the process in the animal cells, the partition of centrioles takes. Centrioles duplicated during interphase but were in the same centrosome.

● Establishment of Bipolarity :

Early in mitosis, the two pairs of centrioles separated. They migrate to opposite sides of the nucleus, establishing the bipolarity of dividing cells.

● Mitotic Apparatus :

Three sets of microtubules (Fibers) arise from each pair of centrioles.

One set of microtubules is called astral microtubules which form asters outward.

The other two set from the spindle in which one

Is kinetochore microtubules and other is

Polar microtubules.

Kinetochore microtubules attach to chromosomes at kinetochores. Polar microtubules do not interact with the chromosomes. They interdigitate with polar microtubules from the opposite side.

These microtubules are made up of a Tubulin protein and traces of

RNA.

Sub stages of Karyokinesis:

During Karyokinesis the various nuclear events have been divided into

Four phases.

1- Prophase

2- Metaphase

3- Anaphase

4- Telophase

Prophase (longest phase) :

▪ During interphase the chromosomes are not visible even with an electronic microscope. Using histological stain for DNA a network of very fine threads can be visualized. This network is called chromatin.

The chromatin material gets condensed by folding. The chromosomes appear as thin threads at the beginning of the prophase.

▪ Chromosomes become thicker and thicker. Ultimately each chromosome is visible having two sister chromatids attached at the centromere.

▪ Towards the end of the prophase nuclear envelope disappear. The nuclear material is released in the cytoplasm, nucleoli also disappear.

▪ Mitotic apparatus is organized.

▪ Cytoplasm becomes more viscous.

Metaphase :

▪Each chromosome is a duplicated structure. It consists of two sister chromatids. These sister chromatids are attached at a point called centromere or primary constriction.

The centromere has a special area the kinetochore. It has a special base arrangement and special protein where kinetochore fibres of mitotic apparatus attach.

▪ The kinetochore fibres of the spindle attach to the kinetochore region, chromosomes align them at the equator of the spindle forming equatorial plate or metaphase plate.

▪ Each kinetochore gets two fibres each from opposite poles.

 Anaphase (smallest stage):

This is the most critical phase of mitosis. It ensures equal distribution of chromatids in the daughter cells.

▪ The kinetochore fibres of the spindle contract towards their respective poles, exert force and their sister chromatids are separated from the centromere.

▪ As a result half-sister chromatids travel towards each pole.

▪ At the same time polar microtubule elongates.

Telophase (Reverse of Prophase):

▪When chromosomes reach opposite poles, the anaphase terminates and telophase begins.

The chromosome's decondense, due to unfolding, ultimately change into chromatin.

▪ Mitotic apparatus is disorganized

▪ The nuclear membrane and nucleoli are reorganized.

▪ The two nucleoli are formed at two poles of the cell.

CYTOKINESIS:
1- Cytokinesis in Animal cell:

During late telophase, the astral microtubules send signals to the equatorial region of the cell. In the equatorial region, actin and myosin are activated. They form contractile rings. It is followed by cleavage furrows which deepen towards the centre of the cell. Thus dividing the parent cell into two daughter cells.

2- Cytokinesis in Plant cell:

At cytokinesis in plants, in place of the contractile ring, a membrane structure phragmoplast is formed from vesicles, which originate from the Golgi complex. These vesicles originate actually during metaphase.

These vesicles line up in the centre of the dividing cell. They fuse to form phragmoplast at the end of telophase. The membrane of vesicles becomes the plasma membrane of daughter cells. These vesicles also contain material for future cell walls such as precursors of cellulose and pectin.

 

SIGNIFICANCE OF MITOSIS:

● Equal Distribution of Hereditary Material:

The equational division is a common division method for the diploid cells only. However, some lower plants and social insects which have haploid cells, also use mitosis for division.

● No change in genetic pieces of information:

As there is no crossing over during cell division, the genetic information remains unchanged generation after generation. Thus continuity of similar information is ensured from parents to daughter cell.

Asexual Reproduction :

All kinds of asexual reproduction take place by mitosis.

● Regeneration :

It involves mitosis.

● Healing of Wounds:

It is also due to mitosis.

● Development and Growth:

The development and growth of multicellular organisms depend upon orderly controlled mitosis.

● Tissue culture and Cloning:

Tissue culture and cloning are done through mitosis.

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