Editing Cell biology (section)

==Growth and development==
=== Eukaryotic cell cycle ===
{{Main|Cell cycle}}
[[File:Animal_cell_cycle-en.svg|thumb|386x386px|The process of [[cell division]] in the animal [[cell cycle]]]]
Cells are the foundation of all organisms and are the fundamental units of life. The growth and development of cells are essential for the maintenance of the host and survival of the organism. For this process, the cell goes through the steps of the [[cell cycle]] and development which involves cell growth, [[DNA replication]], [[cell division]], regeneration, and [[cell death]].

The cell cycle is divided into four distinct [[Cell cycle#Phases|phases]]: G1, S, G2, and M. The G phase – which is the cell growth phase – makes up approximately 95% of the cycle. The proliferation of cells is instigated by progenitors. All cells start out in an identical form and can essentially become any type of cells. Cell signaling such as induction can influence nearby cells to determinate the type of cell it will become. Moreover, this allows cells of the same type to aggregate and form tissues, then organs, and ultimately systems. The G1, G2, and S phase (DNA replication, damage and repair) are considered to be the interphase portion of the cycle, while the M phase ([[mitosis]]) is the [[cell division]] portion of the cycle. Mitosis is composed of many stages which include, prophase, metaphase, anaphase, telophase, and cytokinesis, respectively. The ultimate result of mitosis is the formation of two identical daughter cells.

The cell cycle is regulated in [[cell cycle checkpoint]]s, by a series of signaling factors and complexes such as cyclins, [[cyclin-dependent kinase]], and [[p53]]. When the cell has completed its growth process and if it is found to be damaged or altered, it undergoes cell death, either by [[apoptosis]] or [[necrosis]], to eliminate the threat it can cause to the organism's survival.<ref>{{Cite journal|last1=Shackelford|first1=R E|last2=Kaufmann|first2=W K|last3=Paules|first3=R S|date=February 1999|title=Cell cycle control, checkpoint mechanisms, and genotoxic stress.|journal=Environmental Health Perspectives|volume=107|issue=suppl 1|pages=5–24|doi=10.1289/ehp.99107s15|pmid=10229703|pmc=1566366|bibcode=1999EnvHP.107S...5S |issn=0091-6765}}</ref>

===Cell mortality, cell lineage immortality===
The ancestry of each present day cell presumably traces back, in an unbroken lineage for over 3 billion years to the [[abiogenesis|origin of life]]. It is not actually cells that are [[immortality|immortal]] but multi-generational cell lineages.<ref name="Bernstein2000">Bernstein C, Bernstein H, Payne C. Cell immortality: maintenance of cell division potential. Prog Mol Subcell Biol. 2000;24:23-50. {{doi|10.1007/978-3-662-06227-2_2}}. PMID 10547857.</ref>  The immortality of a cell lineage depends on the maintenance of [[cell division]] potential.  This potential may be lost in any particular lineage because of cell damage, [[cellular differentiation|terminal differentiation]] as occurs in nerve cells, or programmed cell death ([[apoptosis]]) during development.  Maintenance of cell division potential over successive generations depends on the avoidance and the accurate repair of cellular damage, particularly [[DNA damage (naturally occurring)|DNA damage]].  In sexual organisms, continuity of the [[germline]] depends on the effectiveness of processes for avoiding DNA damage and [[DNA repair|repairing those DNA damages]] that do occur.  Sexual processes in [[eukaryote]]s, as well as in [[prokaryote]]s, provide an opportunity for effective repair of DNA damages in the germ line by [[homologous recombination]].<ref name = Bernstein2000/><ref>Avise JC. Perspective: The evolutionary biology of aging, sexual reproduction, and DNA repair.  Evolution. 1993 Oct;47(5):1293-1301. {{doi|10.1111/j.1558-5646.1993.tb02155.x}}. PMID 28564887.</ref>

=== Cell cycle phases ===
The cell cycle is a four-stage process that a cell goes through as it develops and divides. It includes Gap 1 (G1), synthesis (S), Gap 2 (G2), and mitosis (M). The cell either restarts the cycle from G1 or leaves the cycle through G0 after completing the cycle. The cell can progress from G0 through terminal differentiation. Finally, the interphase refers to the phases of the cell cycle that occur between one mitosis and the next, and includes G1, S, and G2. Thus, the phases are:
* '''G1 phase''': the cell grows in size and its contents are replicated.
* '''S phase''': the cell replicates each of the 46 chromosomes.
* '''G2 phase''': in preparation for cell division, new organelles and proteins form.
* '''M phase''': cytokinesis occurs, resulting in two identical daughter cells.
* '''G0 phase''': the two cells enter a resting stage where they do their job without actively preparing to divide.<ref>{{Cite web|title=The Cell Cycle - Phases - Mitosis - Regulation|url=https://teachmephysiology.com/biochemistry/cell-growth-death/cell-cycle/|access-date=2021-10-07|website=TeachMePhysiology}}</ref>