Editing Cell cycle (section)

===G<sub>0</sub> phase (quiescence)===
[[File:Plant cell cycle.svg|thumb|Plant cell cycle]]
[[File:Animal cell cycle-en.svg|thumb|Animal cell cycle]]
{{main|G0 phase}}

G<sub>0</sub> is a resting phase where the cell has left the cycle and has stopped dividing. The cell cycle starts with this phase. Non-proliferative (non-dividing) cells in multicellular [[eukaryote]]s generally enter the quiescent G<sub>0</sub> state from G<sub>1</sub> and may remain quiescent for long periods of time, possibly indefinitely (as is often the case for [[neuron]]s). This is very common for cells that are fully [[cellular differentiation|differentiated]]. Some cells enter the G<sub>0</sub> phase semi-permanently and are considered post-mitotic, e.g., some liver, kidney, and stomach cells. Many cells do not enter G<sub>0</sub> and continue to divide throughout an organism's life, e.g., epithelial cells.

The word "post-mitotic" is sometimes used to refer to both [[G0 phase|quiescent]] and [[Cellular senescence|senescent]] cells. Cellular senescence occurs in response to DNA damage and external stress and usually constitutes an arrest in G<sub>1</sub>. Cellular senescence may make a cell's progeny nonviable; it is often a biochemical alternative to the self-destruction of such a damaged cell by [[apoptosis]].