Mitotic Division

introduction image

Mitotic division shows a pattern of cell division, where a single cell multiplies into two similar daughter cells by the segregation of newly replicated chromosomes in the nucleus. It is the intermediate phase of the cell division that activates after the G-2 interphase and ends with the stage of cytokinesis. Mitosis is a part of the cell cycle defines as a combination of karyokinesis and cytokinesis, and are collectively known as M-phase.

During mitotic cell division, there is no visible cell growth, and a cell uses all its cellular energy to undergo cell division. A term “Mitosis” was given by a scientist named “Walther Flemming” in the year 1882 from a Greek work “Mito” which means thread. Sometimes, term mitosis is interchangeable with the terms like Karyokinesis or equational cell division.

Content: Mitotic Division

    1. Definition
    2. Stages
    3. Importance

Definition of Mitotic Division

The mitotic division defines as a kind of eukaryotic cell multiplication that first carry out nuclear division followed by cytoplasmic division, and finally forms two identical progenies having the same set of chromosomes as of parent. It occurs during the M-phase of the cell cycle that completes along with the phase of cytokinesis. Therefore, the M-phase or mitotic phase generally includes two stages, namely karyokinesis and cytokinesis.
cell cycle showing mitotic phase
Karyogenesis is a stage of nuclear division, which involves an equal division of the daughter chromosomes into two daughter nuclei. Cytokinesis is a stage of cytoplasmic division, which involves a uniform division of the cell cytoplasm (having two daughter nuclei) into two equal-sized daughter cells, each having the same genetic information to that of a parent cell.

Where does Mitosis occur?

Mitosis or mitotic division is a process of cell division that is limited to the animal’s somatic or non-reproductive cells and vegetative plant cells. It does not occur in the animal’s reproductive or germ cells, i.e. sperm and ovum, which only develops via meiosis. Mitotic division generally occurs in the diploid animal cells, whereas in plants it can occur in haploid cells also.

Result of Mitotic Division

The mitotic cell division can produce two diploid cells from a single diploid cell and two haploid cells from a single haploid cell. So, basically, it involves multiplication of cell, where a cell divides, again and again, to produce new identical cells by replacing the old ones.

Stages of Mitosis

Mitotic cell division is a continuous cycle, which involves two stages:

  1. Karyokinesis
  2. Cytokinesis

Karyokinesis

It can define as a process of nuclear division, results in a chromosomal separation where genetic information contained in a chromosome is transferred into the two daughter nuclei. Karyokinesis further includes four sub-stages like:

Prophase

It is the first stage of karyokinesis, which goes through specific changes in a cell. The chromatin fibres coil to form a chromosome that further undergoes duplication. As a result of duplication, the chromosomes condense and appear as two wrapped threads. Thus, the chromosomes possess two thick and short sister chromatids, having a rod shape.
Prophase
Apart from chromatids appearance, the degeneration or break down of a nuclear membrane and nucleolus occurs. As a result of membrane breakdown, the chromosomes formed releases out into the cytosol. The microtubules like kinetochore tubule form a constricted region refers as “Centromere” that unites the two sister chromatids.

Metaphase

Prometaphase: During this phase, a nuclear membrane subsides into small vesicles inside a cytosol. The chromosome carries on to condense and gets shorter and wider. Then the protein structures or microtubules penetrate from centrosome having a pair of centrioles to give rise polar fibres or mitotic spindle. The polar microtubules expand from the end of the cell to the cell’s equator and finally join to the kinetochore. The kinetochore forms centromere attaches to the chromosomal kinetochore fibres.

Late Metaphase: During this phase, the chromosomes shift towards the centre of the central line by forming a metaphasic plate. The alignment of the chromosome on a metaphase plate is a process that refers to as “Congression”.

Metaphase

Anaphase

During early anaphase, a centromere connecting two sister chromatids tends to splits longitudinally as a result of spindle fibre contraction. This cause chromatids to move apart from each other, and now it will be called “Full or daughter chromosome”. On further contraction of spindle fibre, the chromosomes tend to move towards the cell’s pole and may appear in various shapes like J, V, I etc.
anaphaseThe shifting of chromosomes towards the opposite pole cause condensation of kinetochore fibres. During late anaphase, a spindle fibre completely degenerates.

Telophase

In this stage, the chromosomes towards the pole start to uncoil itself and become elongated, achieved by the absorption of water. The nuclear membrane and nucleolus start to appear surrounding the chromosome, and in the late telophase, it completely reappears. Telophase results in the emergence of two nuclei in a single cytoplasmic cell.
telophase

Cytokinesis

It is the process of partition between the cytoplasmic components into two new genetically-like cells. The method of cytokinesis differs in animal cell and plant cell.

Cytokinesis in Animal cell

Cytokinesis in the animal cell occurs via the formation of fissure inwards to the plasma membrane. A cleavage furrow appears by a contractile ring consisting of actin and myosin-II filaments. An internal force is generated by the sliding movement of actin and myosin-II filaments in a contractile ring. The energy released by the contraction is used by a cell to form a fissure.
cytokinesis in animal cell
A GTPase kinase protein directs the assembly and function of the contractile ring commonly refers to as “Rho-A”. The congression of an actin filament is directed by the Rho-A factor, which activates formins.  A Rho-activated kinase rock functions as an effector molecule that promotes the congression of myosin-II filaments. The phosphorylation of GTPase cause contraction of actin and myosin-II filament results in the formation of cleavage furrow that eventually divide a cell into two identical progenies.

Cytokinesis in Plant cell

Cytokinesis in plant cell occurs via the origination of the cell plate in the middle of cytosol. A cell plate forms by the assembly of microtubules along with actin filament vertical plane.
cytokinesis in plant cell
Some membrane sac structures like lysosomes, peroxisomes etc. also assemble with an array of microtubules and fuse to form a structure commonly referred to as “Phragmoplast” or “Cell plate”. A cell plate eventually divides the cytoplasm of a plant cell into two new similar cells.

Importance of Mitosis

The mitotic division is an important process that is the basis for cell growth and maturation to build a multicellular framework by the division in unicellular cells. It helps in the replacement of existing old and injured cells by the regeneration of newly developed cells. Mitotic division forms a basis for the development of unicellular organisms like a hydra, where this kind of cell division forms a bud that eventually detaches to give rise a new vegetative body. Therefore, it is a means for the vegetative propagation in plants.

It results in the formation of two genetically identical progenies similar to the parent cell by both qualitatively and quantitatively or merely it maintains the genetic stability. The mitotic division promotes cell maturation and multiplication of germ cells and makes them ready for the process of meiosis.

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