Cell cycle analysis uses fluorescent dyes to identify a cell’s phase, which changes as it goes through interphase and mitosis. Flow cytometry measures the intensity of fluorescence to determine the amount of DNA in the cell. The resulting histogram shows two peaks, one for G1 and one for G2, with cells in S phase in between. Abnormalities in DNA can also be detected.
Cell cycle analysis is a technique used in biochemical research to identify and analyze the phase of a biological cell. Throughout its life, a cell goes through a series of cyclical phases which are collectively known as the cell cycle. The amount of deoxyribonucleic acid (DNA) in the cell changes according to the phase. In cell cycle analysis, the cell’s DNA is stained with a fluorescent dye, allowing researchers to determine how much DNA is present and where the cell is in its cycle.
The cell cycle consists of two major phases: interphase and mitosis. Interphase is the preparation for cell division, or mitosis, which is also called M phase. Most of the cell’s life cycle is spent preparing for mitosis, which is short by comparison, so interphase is divided in three parts: G1 phase, S phase and G2 phase.
In G1, the cell is primarily concerned with growth. During S phase, the cell’s genetic information in the form of DNA is replicated in preparation for its division into two daughter cells. In G2, the cell prepares for division, leading to M phase. After mitosis, the cell returns to the G1 section of interphase and the cycle begins again. Cells that for some reason stop dividing leave the cycle and exist inertly in what is known as the G0 phase.
The cell replicates its DNA during S phase, so there is twice as much DNA in the cell during G2 and M as there is in G1 or G0. Researchers use this information in cell cycle analysis to determine cell phase. Cell cycle analysis can also reveal abnormalities in cellular DNA.
The technique used in cell cycle analysis is known as flow cytometry. First, a fluorescent dye is introduced into the cell which colors the DNA molecules by chemically binding to them. The researchers then use an instrument called a cytometer to determine the intensity of the cell’s fluorescence. Higher fluorescence indicates that more dye was able to bind and shows that there is more DNA in the cell.
Usually, cell cycle analysis is used on a pool of cells. A type of graph called a histogram is generated from the data, often showing two distinct peaks: one showing the population of cells in the G1 phase and another – twice as high – showing those in the G2 phase. The G2 phase peak is twice as high because cells in that population contain twice the amount of DNA as those in the G1 peak. Cells in S phase, which are still in the process of DNA replication, appear on the graph somewhere between the two peaks.
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