Phases
The cell cycle consists of four distinct phases: G1 phase, S phase (synthesis), G2 phase (collectively known as interphase) and M phase (mitosis). M phase is itself composed of two tightly coupled processes: mitosis, in which the cell's chromosomes are divided between the two sister cells, and cytokinesis, in which the cell's cytoplasm divides in half forming distinct cells. Activation of each phase is dependent on the proper progression and completion of the previous one. Cells that have temporarily or reversibly stopped dividing are said to have entered a state of quiescence called G0 phase.
| State | Description | Abbreviation | |
|---|---|---|---|
| quiescent/ senescent |
Gap 0 | G0 | A resting phase where the cell has left the cycle and has stopped dividing. |
| Interphase | Gap 1 | G1 | Cells increase in size in Gap 1. The G1 checkpoint control mechanism ensures that everything is ready for DNA synthesis. |
| Synthesis | S | DNA replication occurs during this phase. | |
| Gap 2 | G2 | During the gap between DNA synthesis and mitosis, the cell will continue to grow. The G2 checkpoint control mechanism ensures that everything is ready to enter the M (mitosis) phase and divide. | |
| Cell division | Mitosis | M | Cell growth stops at this stage and cellular energy is focused on the orderly division into two daughter cells. A checkpoint in the middle of mitosis (Metaphase Checkpoint) ensures that the cell is ready to complete cell division. |
After cell division, each of the daughter cells begin the interphase of a new cycle. Although the various stages of interphase are not usually morphologically distinguishable, each phase of the cell cycle has a distinct set of specialized biochemical processes that prepare the cell for initiation of cell division.
Read more about this topic: Cell Cycle
Famous quotes containing the word phases:
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—Alexander Herzen (1812–1870)
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—Mrs. H. O. Ward (1824–1899)