Editing Cell cycle (section)

===Interphase ===
{{main|Interphase}}
Interphase represents the phase between two successive M phases. Interphase is a series of changes that takes place in a newly formed cell and its nucleus before it becomes capable of division again. It is also called preparatory phase or intermitosis. Typically interphase lasts for at least 91% of the total time required for the cell cycle.

Interphase proceeds in three stages, G<sub>1</sub>, S, and G<sub>2</sub>, followed by the cycle of mitosis and cytokinesis. The cell's nuclear DNA contents are duplicated during S phase.

====G<sub>1</sub> phase (First growth phase or Post mitotic gap phase)====
[[File:Human karyotype with bands and sub-bands.png|thumb|250px|Schematic [[karyogram]] of the human chromosomes, showing their usual state in the G<sub>0</sub> and G<sub>1</sub> phase of the cell cycle. At top center it also shows the chromosome 3 pair in [[metaphase]] (annotated as "Meta."), which takes place after having undergone [[DNA synthesis]] which occurs in the [[S phase]] (annotated as S) of the cell cycle.<br>{{further|Karyotype}}]]
{{main|G1 phase}}
The first phase within interphase, from the end of the previous M phase until the beginning of DNA synthesis, is called [[G1 phase|G<sub>1</sub>]] (G indicating ''gap''). It is also called the growth phase. During this phase, the biosynthetic activities of the cell, which are considerably slowed down during M phase, resume at a high rate. The duration of G<sub>1</sub> is highly variable, even among different cells of the same species.<ref name="pmid4515625">{{cite journal | vauthors = Smith JA, Martin L | title = Do cells cycle? | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 70 | issue = 4 | pages = 1263–1267 | date = April 1973 | pmid = 4515625 | pmc = 433472 | doi = 10.1073/pnas.70.4.1263 | doi-access = free | bibcode = 1973PNAS...70.1263S }}</ref> In this phase, the cell increases its supply of proteins, increases the number of organelles (such as mitochondria, ribosomes), and grows in size. In G<sub>1</sub> phase, a cell has three options. 
*To continue cell cycle and enter [[S phase]]
*Stop cell cycle and enter [[G0 phase|G<sub>0</sub>]] phase for undergoing [[Cellular differentiation|differentiation]].
*Become arrested in G<sub>1</sub> phase hence it may enter G<sub>0</sub> phase or re-enter cell cycle. 
The deciding point is called [[Cell cycle checkpoint#G1 .28Restriction.29 Checkpoint|check point]] ([[Restriction point]]). This [[Cell cycle checkpoint#G1 .28Restriction.29 Checkpoint|check point]] is called the restriction point or START and is regulated by G<sub>1</sub>/S cyclins, which cause transition from G<sub>1</sub> to S phase. Passage through the G<sub>1</sub> check point commits the cell to division.

====S phase (DNA replication)====
{{main|S phase}}
The ensuing [[S phase]] starts when [[DNA synthesis]] commences; when it is complete, all of the [[chromosome]]s have been replicated, i.e., each chromosome consists of two sister [[chromatid]]s. Thus, during this phase, the amount of DNA in the cell has doubled, though the [[ploidy]] and number of chromosomes are unchanged. Rates of RNA [[Transcription (genetics)|transcription]] and [[Protein biosynthesis|protein synthesis]] are very low during this phase. An exception to this is [[histone]] production, most of which occurs during the S phase.<ref name="pmid7199388">{{cite journal | vauthors = Wu RS, Bonner WM | title = Separation of basal histone synthesis from S-phase histone synthesis in dividing cells | journal = Cell | volume = 27 | issue = 2 Pt 1 | pages = 321–330 | date = December 1981 | pmid = 7199388 | doi = 10.1016/0092-8674(81)90415-3 | s2cid = 12215040 }}</ref><ref name="pmid12370293">{{cite journal | vauthors = Nelson DM, Ye X, Hall C, Santos H, Ma T, Kao GD, Yen TJ, Harper JW, Adams PD | display-authors = 6 | title = Coupling of DNA synthesis and histone synthesis in S phase independent of cyclin/cdk2 activity | journal = Molecular and Cellular Biology | volume = 22 | issue = 21 | pages = 7459–7472 | date = November 2002 | pmid = 12370293 | pmc = 135676 | doi = 10.1128/MCB.22.21.7459-7472.2002 }}</ref><ref name="pmid14018040">{{cite journal | vauthors = Cameron IL, Greulich RC | title = Evidence for an essentially constant duration of DNA synthesis in renewing epithelia of the adult mouse | journal = The Journal of Cell Biology | volume = 18 | issue = 1 | pages = 31–40 | date = July 1963 | pmid = 14018040 | pmc = 2106275 | doi = 10.1083/jcb.18.1.31 }}</ref>

====G<sub>2</sub> phase (growth)====
{{main|G2 phase}}
G<sub>2</sub> phase occurs after DNA replication and is a period of protein synthesis and rapid cell growth to prepare the cell for mitosis. During this phase microtubules begin to reorganize to form a spindle (preprophase). Before proceeding to [[Mitosis|mitotic phase]], cells must be checked at the G<sub>2</sub> checkpoint for any DNA damage within the chromosomes. The G<sub>2</sub> checkpoint is mainly regulated by the tumor protein [[P53 upregulated modulator of apoptosis|p53]]. If the DNA is damaged, p53 will either repair the DNA or trigger the apoptosis of the cell. If p53 is dysfunctional or mutated, cells with damaged DNA may continue through the cell cycle, leading to the development of cancer.