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"Biotechnology: A closer look
Unraveling the mysteries of life"

What resembles a staircase, could be stretched around the earth some 380,000 times, but resides, instead, in our 50 trillion human cells? The answer is DNA, the molecule of life, which spins apart at about 8,000 revolutions per minute to pass genetic information from one generation to another.

DNA has been in the news a lot lately. Whether it is talk of gene therapy, genetically-modified foods or recombinant vaccines, seldom a week passes that we don't hear about some DNA-related process or product and its promised importance in our lives.

As recently as 50 years ago, little was known about DNA beyond its chemical composition. Then in 1953, an American biochemist and a British physicist working together in Cambridge, England, determined the structure of DNA to be long complementary chains of only four different nucleotides twisted like an elegant staircase into a double helix.

"The order of these four nucleotides can be put together in a variety of ways to code for every organism on earth," says Calvin Keeler, professor of molecular virology at the University of Delaware College of Agriculture and Natural Resources. Keeler's work developing vaccines for the poultry industry is centered on DNA research.

"How could only four compounds code for a bacterium or a water buffalo or a human being?" asks Keeler. "It seems too simple," which is one of the reasons, he says, that biologists long believed proteins to be the molecules of inheritance as proteins are long, complex macromolecules. But they were proven wrong in 1953.

Learning the language of life
Keeler uses a simple analogy to describe DNA. "Think about DNA as a book made up of many chapters and sentences," he begins. "There are 26 letters in the English alphabet, but only four letters in the genetic alphabet. Every biological word is made up of a sequence of three DNA letters, or nucleotides.

"These three nucleotides are what we call the genetic code because the nucleotides spell, or code for, one of 20 amino acids. Amino acids are the words that link together to form a sentence, or protein, and proteins do the work of the cell.

"A sentence can be 50 or 60 words long, or it can be thousands of words long; and words can be arranged in an infinite number of combinations," says Keeler, noting that the same DNA is in every cell in an organism. Yet some regulator within this blueprint tells the cell when and where a protein should be made. It tells it how much should be made, the rate at which it is made, and when the protein should stop being made.

"If you take a nose cell, for example, you don't want it to express a gene from a pancreas," says Keeler, explaining that expressed proteins are what make organisms different from one another.

The DNA in every human cell is approximately 3 billion base pairs of nucleotides long, packaged into 23 pairs of chromosomes (we inherit one set from each parent). Compressed within the nucleus of every cell until replication, DNA unwinds to transfer genes to the next generation.

"If our DNA in one cell were stretched out, end-to-end, it would measure about a yard in length," Keeler estimates.

"This is a pretty phenomenal concept," he points out, particularly when you multiply it by our 50 trillion cells from head to toe, which equals an amazing 9 trillion miles of DNA in each and every one of us. Because DNA is so small (you would have to blow it up 20,000 times to see it) molecular research is accomplished not with microscopes, but chemically.

The importance of molecular research
Keeler says our growing understanding of DNA enables scientists to approach a range of health and environmental problems in different ways than ever before.

"My particular research, for example, is centered on evaluating the virus/host reactions between the infectious laryngotracheitis virus (ILTV), a herpes virus, and chickens," says Keeler.

"Because of our DNA research, we are learning how to develop safer vaccines that can signal an immune response without any threat whatsoever of the host getting sick. We also are exploring ways to bolster the immune response of an animal, which is the other side of the equation.

"Genetically engineered vaccines have been used for years to control pseudorabies virus, a disease of swine," Keeler says. "These same techniques are being used to develop vaccines for such human diseases as AIDS."

University of Delaware
College of Agriculture and Natural Resources
2000