Almost all of the cells in our bodies contain the same deoxyribonucleic acid (DNA), with all the same genes. Not all the genes are in use in any particular cell, however. In each cell type, only certain genes are "switched on," so to speak. For example, cells in the liver perform different functions from muscle cells, because different genes are being expressed in them. Microarray technology is a technique that has evolved to allow us to see which genes are being used in each particular class of cells throughout the body.
Microarray technology helps scientists discover which genes are switched on in different cells, and how cells achieve the types of specialization they demonstrate. In a typical microarray experiment, DNA molecules are placed in specific, predetermined spots on a microscope slide. This arrangement of DNA molecules is known as a microarray, since it is very small, and this is where microarray technology gets its name.
Once the microarray has been organized, a type of ribonucleic acid (RNA) known as messenger RNA (mRNA) is isolated from a particular type of cell. The mRNA serves as a working duplicate of one or more genes within a cell, and is thus a good indicator of which genes are being expressed in that cell. When the mRNA has been isolated, a fluorescent dye is added to it to make it more easily visible under a microscope. At this point, the mRNA is added to the DNA microarray on the slide.
When the two types of genetic material are mixed on the slide, the mRNA will stick to the DNA in the place that represents the gene it originally came from. The mRNA will not stick to every gene in the DNA sample, because not every gene is expressed by a cell. Any mRNA which fails to attach to the DNA in the microarray is then washed away, and that which does stick is clearly visible now because of the dye added earlier. The places on the DNA that the mRNA stick to are discrete, known genes. Therefore, this application of microarray technology allows researchers to see which types of genes are expressed by a certain cell type.
The uses of microarray technology are mainly focused in the fields of medicine and biotechnology. Apart from the discovery of genes and those which different cells express, new drugs can also be designed in light of discoveries made by these techniques. Microarray technology also means that diseases, including cancer, can be diagnosed and studied in ways that were previously impossible.
