Cell Division

Life of all multicellular organisms starts from single cell i.e. zygote.

Growth of every living organism depends on cell division.

As stated in the cell theory, every cell arises from the pre-existing cell.

Cell cycle :

Sequential events occurring in the life of a cell is called cell cycle.

There are two phases of cell cycle as interphase and M-phase.

During interphase, cell undergoes growth or rest as per the need.

During M-phase, the cell undergoes division.

Interphase alternates with the period of division.

 

 

 

Interphase :

Interphase is the stage between two successive cell divisions.

It is the longest phase of cell cycle during which the cell is highly active and prepares itself for cell division.

The interphase is divisible into three sub-phases as G1-phase, S-phase and G2-phase.

 

G1-phase :

This is also known as first gap period or first growth period.

It starts immediatelyafter cell division. Cell performs RNA synthesis (mRNA, rRNA and t-RNA), protein synthesis and synthesis of membranes during this phase.

 

S-phase : It is synthesis phase in which DNA is synthesized or replicated, so that amount of DNA per cell doubles.

Histone proteins are also synthesized during this phase.

 

G2 phase :

G2 is the second growth phase, during which nucleus increases in volume.

Metabolic activities essential for cell division occur during this phase.

Various proteins necessary for cell division are synthesized during this phase.

Besides, RNA synthesis also occur during this phase.

In animal cells, a daughter pair of centrioles appear near the pre-existing pair.

M-phase or period of division :

'M' stands for mitosis or meiosis.

M-phase involves karyokinesis and cytokinesis.

Karyokinesis is the division of nucleus into two daughter nuclei whereas cytokinesis is division of cytoplasm resulting in two daughter cells.