BUSINESSWEEK ONLINE : JUNE 12, 2000 ISSUE
COVER STORY

The Genome Explained
The information in the genetic code is used to make proteins--the real workhorses of the cell

The genome of an organism is its instruction book: It contains all the genes needed for life. Genes are made up of DNA, the famous double helix, and they reside on long, densely packed fibers called chromosomes. Only 3% of the genetic information in the human genome represents genes. A tiny bit of the remaining 97% contains control regions that tell genes when to turn on and turn off. The rest is called junk DNA, because it has no apparent function.

The information encoded in genes must be copied into RNA, a close cousin of DNA, and then used to assemble proteins, the real workhorses of the cell. Hemoglobin, which carries oxygen through the bloodstream, is one example. Proteins have their own code, which is more complex than the genetic code. Among the things the protein code does is knot the molecules into the complicated shapes necessary for them to function properly.

The sequence of building blocks--called bases--in DNA determines the nature of the protein that will be assembled from a given gene. A mistake in a single base in a gene that is thousands of bases long can lead to serious disease. Sickle-cell anemia is one example of a single-base mutation, called a point mutation. Other illnesses, such as heart disease and obesity, are more complex, resulting from particular combinations of genes.

If every cell in the human body has the same genetic information, what makes a heart cell different from a muscle cell? Specific genes are flipped on at different times in different tissues. Figuring this out is a daunting task: Researchers are using semiconductor-like DNA chips to help automate the process.

By Ellen Licking

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