DNA FOR DUMMIES: THE BASICS YOU NEED TO KNOW The blueprint of life is DNA. Its famous double helix is a long, long chain built by linking together four simple molecules. The order in which those molecules are linked determines the information contained in the DNA. It is the SEQUENCE of those molecules that molecular biologists are now busily decoding. All of the DNA in an organism is referred to as the organism's GENOME. GENES are DNA chains made up of hundreds or thousands of simple molecules. Each gene contains instructions to make another type of crucial molecule, a PROTEIN. Proteins include everything from hormones such as insulin--which regulates blood-sugar levels--to enzymes that help digest the food we eat. Some proteins turn other genes on and off, which then affect still other genes, creating complicated feedback loops. Individual proteins are but tiny cogs in incredibly complex biological systems. Consider the immune system, in which thousands of genes and proteins work together to field an army of cells and antibodies (another type of protein) against intruders. The DNA in each of the body's cells contains all the genetic information to produce a person. But in any given cell, only some of the genes are switched on; the rest are dormant. That's what makes a liver cell, say, different from a skin cell--different sets of genes are turned on in each. Scientists despair of understanding exactly how humanity's 80,000 genes flip on and off in the amazing molecular dance that leads to a human being. But they are uncovering the genes and proteins that underlie small pieces of this grand puzzle--so-called BIOLOGICAL PATHWAYS. One famous pathway is the process by which cells turn the sugar glucose into enough energy to run a marathon. But genes can also go horribly wrong. A ''misspelling'' in just one letter--an improper or missing link in the DNA chain--is a MUTATION. A change in a single link of the thousands in a gene can produce disease. Sickle-cell anemia, for instance. Other diseases are more complex. Heart disease, cancer, and Alzheimer's are due to mutations in several genes. Much of the effort in genetics today is directed at finding these faulty genes--and then figuring out how their flawed proteins make biological pathways go awry. Aiding the search is something called a GENETIC MAP. Much like an atlas, a genetic map shows the locations of genes and fragments that have been identified. Each of these can be used as a signpost, or MARKER, to help identify genes that might be related to disease. Just as it's easier to get to Evanston if you know it's near Chicago, it's easier to find a gene if you start from a marker nearby. When gene sleuths are tracking an inherited disease in a family, they look for markers present only in family members with the disease. When they find those markers, they know they are close to the genes. Finding genes this way is costly and time-consuming. That's why researchers have begun blindly sequencing the entire genome, link by link. That way they will find thousands of new genes and all of the extra genetic information that sits between genes. This vast amount of new information opens the door to the most basic understanding of life. By John Carey in Washington Return to main story

Updated June 15, 1997 by bwwebmaster
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