DNA microarray: Difference between revisions

Revision as of 19:07, 21 August 2003

Revision as of 07:32, 12 October 2003

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"Microarray" refers not only to GeneChips but also to chips that use much longer probe sequences, such as the entire [[gene]]s that may be contained on [[cDNA]]s. Because, Affymetrix owns a [[patent]] both on the use of oligonucleotide probes as well as on a means to affix them to chips, microarrays not made by Affymetrix are manufactured by a different technique that is non-proprietary.

Typically arrays are used to detect the presence of [[mRNA]]s that may have been [[transcription|transcribed]] from different genes and which encode different proteins. The RNA is extracted from many cells of a single type, then converted to cDNA and "amplified" in [[concentration]] by [[reverse transcriptase|rt]][[RT-PCR|rtPCR]]. [[Fluorescent tag]]s are chemically attached to the strands of DNA. A cDNA [[molecule]] that contains a sequence complementary to one of the single-stranded probe sequences will stick via ''base pairing'' (more at [[DNA]]) to the spot at which the complementary probes are affixed. The spot will then [[fluorescence|fluoresce]] (or glow) when examined.

The glow indicates that cells in the sample had recently transcribed a gene that contained the probed sequence ("recently," because cells tend to degrade RNAs soon after transcribing them). The intensity of the glow depends on how many copies of a particular mRNA were present and thus roughly indicates the ''activity'' or ''expression level'' of that gene. So arrays in a sense paint a picture or "profile" of which genes in the [[genome]] are active in a particular cell type and under a particular condition.