A cDNA microarray is a method of identifying active genes in a cell. It uses small DNA sequences that attach to RNA sequences and are labeled with fluorescent labels. The test identifies which genes are expressing more than others and which are not expressing at all. It is useful for distinguishing genes that act differently in various cell types and conditions such as cancer. The test is usually done by machine and commercial companies make cDNA microarray plates for laboratories.
A cDNA microarray is a method of figuring out which genes in a cell are active at any one time. This is useful for distinguishing which genes act differently in various cell types and also which genes are active in certain conditions, such as cancer. The name cDNA comes from the use of small deoxyribonucleic acid (DNA) sequences that attach to ribonucleic acid (RNA) sequences that cells express. These small DNA sequences are complementary (c) to the RNA sequences, hence the stickiness, and are also labeled with fluorescent labels, so an experimenter can see which RNA sequences are expressed and to what extent.
Cells contain DNA as a template for all the proteins a cell needs. The DNA sequence represents the amino acids that the body needs to collect and put together to form a protein. There is an intermediate step between DNA and protein production. The cell copies the gene sequence into another form called messenger RNA (mRNA). Then, the cell’s machinery reads the mRNA as instructions for the desired protein.
Because the mRNAs of particular genes are not all expressed continuously, geneticists can observe what is expressed under certain conditions. A useful approach is to compare cancer cells with healthy cells and see which genes express mRNA differently in the two situations. This information can then point scientists towards targets for treatments. Different cell types also produce different mRNA templates, as each cell type has a different job.
The basis of a cDNA microarray is that the test identifies the mRNA expressed by a sample at a sensitivity that allows the experimenter to understand which genes are expressing more than others and which are not expressing it at all. Because a cDNA microarray usually tests hundreds of thousands of mRNA sequences, it is usually done by machine. The analyst does not directly use the mRNA that he extracts from a cell, but rather makes a copy of that mRNA as a DNA sequence.
Commercial companies make cDNA microarray plates for laboratories. They create the DNA sequences that correspond to the hundreds or thousands of genes the experimenter wishes to test and place each one individually on a single microarray slide. This represents all genes that could be expressed in that group.
Complementary sequences to the mRNA that the researcher extracts from the cell are then made in the laboratory by copying the RNA into DNA. These products have a sequence that attaches to the DNA on the microarray slide that would have produced the mRNA. The analyst then attaches the fluorescent molecules to these cDNA sequences.
Covering the microarray slide in the cDNA allows any complementary sequences to adhere. The slide is then washed to remove unbound cDNA. A scanner then measures the amount of fluorescence, if any, on each individual DNA dot. Genes that express more mRNA will have more fluorescent cDNAs bound to them than genes that express less mRNA. This way, the analyst can figure out which genes are more active than others and compare the results with a different cell type.
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