A gene is a stretch of DNA that codes for the creation of a particular protein, such as an enzyme. The DNA of any living cell contains all the genes that cell or organism will ever need. So how does a cell "decide" when to retrieve particular data from the genome?
Certain proteins, known as regulatory proteins, control the genes so that only necessary proteins are produced. These proteins bind to short stretches of DNA, appropriately positioned in the genome, usually 'upstream' of the gene being regulated. By doing so, they can recruit another protein complex, called the RNA polymerase, to start copying the DNA into RNA, or block it from doing so.
While the regulatory proteins are important, the short DNA sequence is equally important. These are called regulatory elements or regions. Research to find all regulatory regions in the genomes of all sorts of organisms is under way.
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