Mitosis

Mitotic cell division is first described by W.flemming in 1882(in plant cell by Strasburger).Karyokinesis(DNA duplication followed by nuclear division) followed by cytokinesis(cytoplasm of single eukaryotic cell is divided to form daughter nuclei).

Amitosis:
This type cell division is usually occurs in prokaryote. Its a simple type of cell division.All the cell contents including nucleus divide into two equal halves by means of inwardly growing constriction in the middle of the cell.

In Plant,mitotic cell division occur at apical(top portion of plant)

In higher animals,the process is distributed all over the body.

Phases of mitotic cell division

  1. Interphase(subdivided into G1,S and G2 phases) is a long phase.
  2. Short M stage(mitotic stage consist of  prophase,metaphase,anaphase and telophase)
  3. cytokinesis.
Note: Duration of occurrence of Interphase and mitotic stage may differ in different cells.
Interphase:
                During this phase the cell prepares itself for cell division process.Synthesis of nucleic acids and proteins occurs.Chromosomes appears as network of chromatin.It include three sub stages namely.
1)G1(Gap1 phase)
                           Starts immediately after cell division.cell grows in size as new proteins and RNA are synthesized for various metabolic activities.Non-dividing cell does not proceed beyond G1 phase.Differentiating cells are said to be in G0 phase.
2)S(synthetic pahse)
                              Duplication of DNA occurs during this phase.Each chromosomes now composed of two sister chromatids.
3)G2(Gap2 phase)
                            Spindle fibres are formed during this stage using proteins.

mitotic cell division
Mitosis

Mitosis by Jpablo cad translated by Matt (CC BY-SA)

Mitotic phase:
                    Its subdivided into four stages
1)Prophase:
  • Chromatin network begins to coil
  • Chromosomes becomes distinct as long thread like structure.
  • Each chromosome has two chromatids side by side held together by centromere.
  • Nucleus and nuclear membrane starts dissapearing.
2)Metaphase:
  • Nuclear membrane and nucleolus disappearance marks the beginning of metaphase.
  • Chromosomes becomes shorter by further coiling.
  • At this stage only chromosomes are distinct and visible under compound microscope.
  • all centromeres are aligned in equatorial  position.
  • Two chromatids facing each one pole and other facing opposite.
  • spindle fibres(made of protein rich in sulphur containing amino acids) are attached to the centromere.
  • During late metaphase centromere  divides results in dision of chromatids of each chromosome.

3)Anaphase:

  • Beginning of anaphase can be characterized by division of centromere.
  • Two groups of chromosomes are pulled towards opposite poles by contraction of spindle fibres.

4)Telophase

  • Thus chromosomes reached the opposite poles at the end of anaphase.
  • They uncoil and elongate results in disappearance(thin and invisible)
  • Now  two daughter nuclei are formed one at each pole.
Cytokinesis:
  • Cytokinesis is the process by which cytoplasm is divided and followed by nuclear division and formation of cell wall betwee two daughter nuclei.
  • Phragmoplast(cell plate) formed by aggregation of vesicles formed by golgi apparatus.
  • Vesicles contains cell wall materials fuse with one another to form cell membrane and cell walls.
At the end Two identical daughter cells are formed as a result of Mitosis.
Significance of mitotic cell division:
  • Two identical daughter cells formed which is identical to mother cell
  • Daughter cell posses genetical identity both qualitative and quantitative.
  • A sexual reproduction in lower plants through mitosis.
  • Continuation of organism
  • Chromosome number is maintained by mitosis in each species
  • Helps in regeneration of body tissues and healing wounds.

By | 2014-07-18T08:06:25+00:00 May 29th, 2013|Cell cycle|0 Comments

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