= Cell cycle
{wiki}
The <cell cycle> is the sequence of events by which a <biological cell> prepares for and completes division, including <DNA replication> and distribution of <chromosomes>. In <Saccharomyces cerevisiae>, changing bud appearance provides an accessible readout; see the Burgess, Powers and Mell account and Hartwell, Culotti and Reid's primary study cited there.
For a typical cycling <diploid> <eukaryotic> <biological cell>, the order is <G1 phase>, <S phase>, <G2 phase>, then <M phase>. <DNA replication> doubles nuclear <DNA> amount during <S phase>; <mitosis> distributes the copies, and <cytokinesis> separates the daughters. The useful distinction is between copying a library and allocating its copies: <DNA replication> changes how much material exists, whereas division changes which <biological cell> contains it.
\Image[/cell-cycle-phases-and-dna-content.png]
{title=The <cell cycle>: copying nuclear <DNA> once, then distributing it to two daughters}
{description=Original schematic for a typical cycling <diploid> <eukaryotic> <biological cell>. Each box states nuclear <DNA> content and <chromosome> count; <M phase> is summarized by its completed daughters. Arrow lengths do not represent phase durations. The <G0 phase> branch shows reversible withdrawal where re-entry is possible, rather than claiming that all nondividing <biological cells> can return.}
<Gene expression> continues to supply <RNA> and <proteins> as the <biological cell> grows; it is different from duplicating the <genome>. In the <yeast cross-species complementation experiment>, restored growth requires successful repeated <cell cycles>, but growth alone does not locate a defect within a phase. Bud appearance in <Saccharomyces cerevisiae> provides another readout, while a <flow cytometric DNA-content assay> asks how much nuclear <DNA> is present and <DNA pulse labeling> asks whether new <DNA> was synthesized during an exposure.
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