Gene Chips
This is not research into nutrition but describes a powerful technique called a microarray that can be used to visualise directly which genes are activated and when. In essence the “chips” are made by fixing single stranded genes to a slice of glass not unlike a silicon chip used in microelectronics. Each chip is subdivided into a grid pattern and one copy of a gene is precisely located, one gene per grid sector. A typical chip measuring about ¾ of an inch square can contain upwards of10,000 different genes, which is about a third of all the genes in the human genome. (Some chips can contain up to 1,000,000 genes.)
Researchers who are interested in finding out which genes are active in a particular cell type or tissue at a particular time can “freeze” the contents of these cells and, by a variety of treatments, extract a particular kind of genetic product called mRNA. The mRNA made by each gene is unique to that gene and is only present when the gene is actively working. If the gene is “switched off” it will not produce any mRNA. The extracted mRNA is further processed to create a fluorescent probe. When these fluorescent probes are introduced to the gene chip the probes will bind only to the sector of the chip containing a copy of the gene from which they were derived in the cell. By knowing which gene has been laid down in each grid sector and noting which sectors have attracted a fluorescing probe it is possible to say which genes were active at the time the cell contents were extracted.
Investigators using gene chips can vary the conditions under which cells are grown to see how different treatments switch on (upregulate) or switch off (downregulate) different genes. Equally they can use microarrays to compare the differences in gene activity between different kinds of tissue in the body and also between healthy and diseased tissues.
