CEll CyclE
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The cell cycle consists of the mitotic (M) phase alternating with interphase. Interphase is divided into G1, S (chromosomes duplicate), and G2 phases (last part of interphase). The M phase is divided into prophase, prometaphase, metaphase, anaphase, telophase, and cytokinesis. The time frame in which G1, S, and G2 occur vary.
Interphase
G1 Phase
The G1 phase is an intermediate phase occupying the time between the end of cell division in mitosis and the beginning of DNA replication during S phase. During this time, the cell grows in preparation for DNA replication, and certain intracellular components, such as the centrosomes undergo replication. Before a cell begins DNA replication, it must ensure that it is biologically ready to take on such a process. G1 is the phase when this cellular monitoring takes place.
S Phase
S phase is the phase of the cell cycle when DNA packaged into chromosomes is replicated. Replication allows for each cell created by cell division to have the same genetic make-up. Once DNA replication is complete the cell contains twice its normal number of chromosomes.
G2 Phase
The G2 phase is a time for the cell to ensure that it is ready to proceed in the cell cycle. G2 is the cell's final chance to grow before it is split into two independent cells during mitosis.
g0 phase
This is where the cell remains indefinitely until the cell cycle begins again, yet not all cells are continually replicated. Non-replicating cells are found in a stage of the cell cycle called G0. These cells may be quiescent (dormant) or senescent (aging or deteriorating). Such cells generally enter the G0 phase from G1. This includes nerve and muscle cells.