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:
“But parents can be understanding and accept the more difficult stages as necessary times of growth for the child. Parents can appreciate the fact that these phases are not easy for the child to live through either; rapid growth times are hard on a child. Perhaps it’s a small comfort to know that the harder-to-live-with stages do alternate with the calmer times,so parents can count on getting periodic breaks.”
—Saf Lerman (20th century)
“That man is to be pitied who cannot enjoy social intercourse without eating and drinking. The lowest orders, it is true, cannot imagine a cheerful assembly without the attractions of the table, and this reflection alone should induce all who aim at intellectual culture to endeavor to avoid placing the choicest phases of social life on such a basis.”
—Mrs. H. O. Ward (1824–1899)
“This socialism will develop in all its phases until it reaches its own extremes and absurdities. Then once again a cry of denial will break from the titanic chest of the revolutionary minority and again a mortal struggle will begin, in which socialism will play the role of contemporary conservatism and will be overwhelmed in the subsequent revolution, as yet unknown to us.”
—Alexander Herzen (1812–1870)