The cell cycle is an orderly sequence of events by which a growing cell duplicates its contents and divides into two. In other word, the life cycle of any specific cell is called as cell cycle It was first described by Howard and Pelc (1953). The cell cycle is a complex and cyclic process of eukaryotic cells. It includes cell growth, duplication of genome, nuclear division & cytoplasmic division. The cell cycle of a somatic cell consists of two phases viz. –
(A) Interphase and
(B) Mitotic phase (M-phase)
Interphase:
It is the metabolically active phase that is further divisible into 3 phases viz. -G1 phase, S-phase & G2 phase.
- G1 phase [Gap-1 phase]
It is the longest phase of interphase. The chromosomes are found in the form of invisible chromatin network. Synthesis of the proteins and RNA which are required for DNA replication. The DNA value is 2C.
- S-phase [Synthetic phase]
There is Synthesis of DNA by replication. 1 he DNA value will increase gradually. There is duplication of centrosome.
- G2 Phase [Gap 2-phase]
There is synthesis of RNA and proteins which are required during mitosis. No DNA replication and the DNA value becomes 4C. There is duplication of cytoplasmic orgenelles.
In G1 – phase, the cell decide to divide or not to divide.
During this phase, the cell enters into prophase, metaphase, anaphase and telophase and finally forms two daughter cells.
