View source for S phase

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The '''S phase''', short for '''synthesis phase''', is a period in the [[cell cycle]] during [[interphase]], between [[G1 phase]] and the [[G2 phase]]. Following G1, the cell enters the S stage, when [[DNA]] [[DNA synthesis|synthesis]] or [[DNA replication|replication]] occurs. At the beginning of the S stage, each [[chromosome]] is composed of one coiled DNA [[double helix]] [[molecule]], which is called a [[chromatid]]. At the end of this stage, each chromosome has two identical DNA double helix molecules, and therefore is composed of two sister chromatids. During S phase, the [[centrosome]] is also duplicated. These two events are unconnected, but require many of the same factors to progress. The end result is the existence of duplicated genetic material in the cell, which will eventually be divided into two.

Damage to DNA often takes place during this phase, and [[DNA repair]] is initiated following the completion of replication. Incompletion of DNA repair may flag [[cell cycle checkpoint]]s, which halts the cell cycle.  However, after the cell has completeted this phase, it is very likely that the cell will continue on to complete the [[cell cycle]].

==See also==
* [[S phase index (SPI)]]

{{Cell cycle}}

[[Category:Cell cycle]]

[[it:Fase S]]

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