Cell Cycle and Cell Division
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It lasts more than 95% of the duration of cell cycle. Interphase has 3 phases :
(a) G1 phase (Gap 1 ) : First growth phase. It is the interval between main
events: mitosis and DNA replication.
There is :-
Continuous growth of cell.
Cell becomes metabolically active.
Prepares machinery for the DNA replication.
Synthesizes RNA and proteins.
(b) S (Synthesis) phase:
It is the longest phase. (NEET-11 2016)
DNA replication takes place.
Amount of DNA per cell doubles. But chromosome number is not
increased i.e. if amount of a DNA in a cell is denoted by 2C it becomes
4C while the no. of chromosomes in a diploid cells denoted by 2n
remains same i.e. 2n.
In animal cells, replication begins in the nucleus, and the centriole
duplicates in the cytoplasm.
(c) G2 phase (Gap 2):
Second growth phase. Cell growth continues.
Synthesis of RNA and proteins continues.
Cell is prepared for mitosis.
2. M PHÅSË (MÏTØSÏS PHÅSË)
MÏTØSÏS
01
It represents the actual cell division (mitosis). It is the
cell division occurring in somatic cells.
It is also called as equational division as the
number of chromosomes in the parent and
progeny cells is same.
02
Mitosis is generally seen in diploid cells. It also
occurs in haploid cells of some lower plants and
some social insects.
03
It is the most dramatic period of the cell cycle as it
involves major reorganization of all cell components. 04