Cell cycle analysis is a technique that is used in biochemical research to identify and analyze the phase of a biological cell. During its lifetime, a cell passes through a series of cyclical phases that collectively are known as the cell cycle. The amount of deoxyribonucleic acid (DNA) in the cell changes based on the phase. In cell cycle analysis, the cell’s DNA is stained with a fluorescent dye, allowing researchers to determine how much of the DNA is present and where the cell is in its cycle.
The cell cycle consists of two broad phases: interphase and mitosis. Interphase consists of preparation for the division of the cell, or mitosis, which is also called the M phase. Most of the cell’s life cycle is spent preparing for mitosis, which is brief by comparison, so interphase is subdivided into three parts: G1 phase, S phase and G2 phase.
In G1, the cell is mainly concerned with growth. During the 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 into the 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 the S phase, so there is twice as much DNA in the cell during G2 and M than there is in G1 or G0. Researchers use this information in cell cycle analysis to determine the cell phase. Cell cycle analysis also can 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 that stains the DNA molecules by chemically binding to them. Researchers then use an instrument called a cytometer to determine the intensity of the cell’s fluorescence. A higher fluorescence indicates that more dye was able to bind, and it shows that there is more DNA in the cell.
Usually, cell cycle analysis is used on a grouping of cells. A type of chart called a histogram is generated from the data, often showing two distinct peaks: one that shows 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 the cells in that population contain twice the amount of DNA as those in the G1 peak. Cells that are in the S phase, which are still in the process of replicating DNA, show up on the graph at an intermediate level between the two peaks.