CELL DIVISION | CELL CYCLE

As we've discussed within the earlier chapter, the cell cycle amazingly follows a daily timing mechanism. Most eukaryotic cells live consistent with an indoor clock, that is, they proceed through a sequence of phases, called the cell cycle.

During the cell cycle DNA is duplicated during the synthesis (S) phase and the copies are distributed to the daughter cells during mitotic (M) phase. Most growing plant and animal cells take 10-20 hours to double in number and a few duplicate at a way slower rate.






A multi cellular organism usually starts it’s life as a single cell (zygote). The multiplication of this single cell and it’s descendants determine the expansion and development of the organism and this is often achieved by cellular division . Cell division may be a complex process by which cellular material is equally divided between daughter cells. Cell division in living things are of three kinds.
They are - 

1. Amitosis
2. Mitosis 
3. Meiosis.


Amitosis

It is an easy sort of division where the cell contents including nucleus divide into two equal halves by an inwardly growing constriction within the middle of the cell. This type of cell division is common in prokaryotes.







Mitotic cell cycle

It is represented by DNA duplication followed by nuclear division (Karyokinesis) which successively is followed by cytokinesis. Mitotic cell division was first described by W. Flemming in 1882. Mitosis in plants was described by Strasburger, in the same year1982. In plants, active mitotic cell division takes place in shoot and root apices. In higher animals mitotic cellular division is claimed to be diffused, distributed everywhere the body.

Mitotic cell cycle consists of long interphase (which is sub divided into G1,S and G2 phases), a brief M stage( or mitotic stage, subdivided into prophase,metaphase, anaphase and telophase) and cytokinesis.The duration of M-phase and Interphase varies in several cells.

Source wikipedia

Interphase

It is the stage in between two successive cell divisions during which the cell prepares itself for the method by synthesizing new nucleic acids and proteins.Chromosomes appear as chromatin network. Interphase consists of the following three sub stages.







i) G1 or Gap –1 Phase

This phase starts immediately after cell division. The cell grows in size and there's synthesis of latest proteins and RNA needed for various metabolic activities of the cell. A non-dividing cell doesn't proceed beyond G1 Phase. The differentiating cells are said to be in G0 Stage .


ii) S- or Synthetic Phase

During this phase there is duplication of DNA. Thus each chromosome now is composed of two sister chromatids.








iii) G2 or Gap –2 Phase

The proteins responsible for the formation of spindle fibres are synthesised during this stage.