Karen Anne Cox, age 13, of Watonga, Oklahoma, for her question:
What exactly is the DNA molecule?
Future historians may write of our times as the early beginnings of true human civilization. They may see us as awaking from the long nightmare of slavery under the hostile laws of nature. If so, they may pinpoint the dawn of true civilization with the discovery of the miraculous molecule we call DNA.
A molecule is a glued package of neatly interlocked atoms. In most nonliving substances, single molecules throng together to form solids, liquids and gases. Plants and animals form more complex materials of small molecules linked together in long, durable chains. These super giant molecules form hydrocarbon chemicals made from chains of packages containing atoms of hydrogen, carbon and other basic elements. We call such giant molecules polymers. Our clever chemists have learned how to assemble many more useful polymers than nature creates. We use them to make our wondrous assortment of plastics.
The fascinating new fields of molecular biology and X -ray crystallography explore the living cell for more miraculous polymers. The cell is a semi fluid unit of turbulent chemical activity. But its hard core is a quiet, tiny nucleus. This is the center that orders and directs the busy cellular activity. Here we, find the genes and chromosomes that carry the blueprint of instructions inherited from generation to generation. In the last decade, researchers found the very molecule that carries these detailed instructions of biological features and behavior, health and disease and even mental tendencies. They called this polymer substance deoxyribonucleic acid and shortened the name to DNA.
The DNA polymer is a sort of rope ladder structure with a series of rungs linking its two stringy sides. The pliable structure is twisted in a spiral shape called a double helix. The basic ingredients are atoms of common elements packaged in small, fairly simple molecules. But the arrangement of these molecules is neither common nor simple. It forms the miraculous substance that governs the vital processes of life in every plant and animal cell. The sides of the ropy ladder are molecules of simple sugars and phosphates. The rungs are nitrogen compounds called bases.
Only four different bases are used to link the DNA polymer. They are chemical compounds called adenine and thymine, cytosine and guanine. Scientists shorten their names to A and T, C and G. Each ring, is a link of two different bases. But A locks only with T and C links only with G. A rung may be TA or AT, CG or GC. These four ties can be arranged in countless different series for example two ATs followed by six GCs, another AT, a CG and two TAs and so on. The order of the bases carries the coded blueprint of life processes in DNA. One human DNA molecule may contain 10,000 rungs. The spiraled and tightly folded DNA in the tiny nucleus of one human cell is about a yard long. The total ladder of DNA in a man's body is about 10 billion miles.
In the 1960s, six Nobel Prizes were awarded to the researchers who discovered the basic structure of DNA. Experts are now tackling the big job of finding how it works. They report that the sequences of the bases are inherited coded messages that govern the behavior of the cells in a living plant or animal. Experts hope someday to read these codes and perhaps change them. Someday they expect to alter DNA patterns to get rid of certain diseases. Perhaps they can give us healthy, long lasting bodies with alert minds to enjoy the wonders of human life to the very brim.