Cell cycle is a ubiquitous, complex sequence of events leading to growth and proliferation of cells. Cell cycle of most eukaryotic cells is divided into four discrete phases: M, G1, S, and G2. S phase is the period during which DNA replication occurs. The cell grows throughout interphase, which includes G1, S, and G2.
Cells at different stages of the cell cycle can also be distinguished by their DNA content. The DNA content of cells duplicates during the S phase (2n to 4n) and DNA content then remains at 4n for cells in G2 and M, decreasing to 2n after cytokinesis.
Experimentally, cellular DNA content can be determined by incubation of cells with a fluorescent dye that binds to DNA, followed by analysis of the fluorescence intensity of individual cells in a flow cytometer. The fluorescence signal is proportional to cellular DNA content.
Propidium iodide is a fluorescent molecule that binds nucleic acid with little or no sequence preference. Because Propidium iodide binds RNA as well as DNA, RNase A is included in this kit to digest cellular RNA and thus decrease background RNA staining from the experiment.
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