Cell cycle
All multicellular organism start life as a single cell the fertilized egg and grown by addition of new cell. The new cell arise by the division of Pre existing cell . This was first suggested by Rudolf Virchow (1958).
When the number of chromosome is reduced to half in gametes as compared to their parent cell, the division is termed as miosis.
The mode of cell division is fundamentally similar in all organism . This emphasises the unity of life . A cell divides when it has grown to a certain maximum size which distributes the kryoplasmic or kernplasma ratio. Cell division is also controlled by a certain agent, factors or substance that triggers cell division. It is also called mitogen .
Daughter cell formed after the division of parent cell main grow in size and divide again the period between two successive division is called generation time. It varies from a few minute to a few days depending upon the type of cell and its environmental condition.
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Cell cycle
The sequence of events by which a cell dublicates its genome and synthesise other cell contains and eventually divides into two daughter cell is termed as cell cycle. A typical eukaryotic cell (example human cell) divides approximately about 24 hours . Howover this time span varies from organism to organism and also from cell to cell types. Cell cycle consist of two stage , a non-dividing growing interphase or I- phase and a short dividing mitotic or M- phase.
Interphase [I- phase]
{Inter -- between, phases-- aspect}
Interphase is a series of change that occur in a newly formed cell and its nucleus before it becomes capable of dividing again. Therefore it is also called intermitosis. It is a non-dividing stage of the cell and its nucleus is called interphase nucleus. Priviously this stage is called 'resting stage' but is in fact a period of great activities.
Three important process which are preparatory to cell division take place during interphase , the process are are-
1} Replication of DNA along with the synthesis of basic nuclear protein and histone.
2} In animal cells , the centriole divides to form a pair of new centrioles. Duplication of centrioles take place by the outgrowth of daughter centrioles from the parents centrioles , which are at right angle to each other.
3}Synthesis of energy rich compounds which provides energy for mitosis and synthesise of protein at the end of the interphase.
Interphase take approximately 95% of the total duration of the cell cycle and last for 10 to 20 hours where's the dividing part take only about an hour. Interface further divisible into three stage G1- phase ,S- phase and G2- phase.
G1-phase
It is also called first growth phase or mitotic gap phase. During this phase the cell growth in size and there is an activity synthesise of RNA and protein . In this phase the cell carries out its psychological function and prepare the machinery needed for all cell to proceed to the next stage. A large number of nucleotide amino acid of for histone synthesis and energy rich compounds are formed cell .Organelle also increase in numbered however it shows no change in the DNA content .
G-2 Phase
It is also called synthetic face in this phase DNA molecules of each chromosome replicates by the synthesise of DNA contain double and duplicate set of gene are formed . Along with DNA chromatin fibre also replicates.
S-phase is also called invisible phase of mitosis, since in this phase chromosome prepare themselves for equitable distribution later on. The centriole is also divides into two centriole pairs in these cell containing the same.
G1- phase
It is also called second growth phase or Pre mitotic gap phase . The synthesis of RNA and protein continue in this phase and the cell prepared itself to go into the mitotic phase. The phase produce micro molecules of cell organelles, spindle formation and cell growth. During G2 Phase a cell contains double DNA content .
Mitotic Phase [M- phase]
Mitotic Phase or M- phase follow the interface and represent the phase of actual division. It consists of karyokin
