Close to the Mystery

Every living cell contains a minuscule amount of an extraordinary substance called DNA (for deoxyribonucleic acid) that carries in it the traits of heredity. When its home cell begins to divide, the DNA performs wondrously: its complicated molecules, ordinarily like two ropes twisted together, untwist and separate. Each rope attracts bits and pieces from fluid around it and forms a new double helix like the original one. Apportioned between the halves of the dividing cells, the duplicated DNA molecules determine whether the new individuals will be men or muskrats, pine trees or pineapples. The hereditary characteristics of the next human generation--of about three billion people--will be controlled by one fifteen-thousandth of a cubic inch of DNA.

In the latest issue of Proceedings of the National Academy of Sciences, two groups of Harvard biochemists, one led by Dr. Julius Marmur, the other by Dr. Paul M. Doty, published reports titled: "Strand Separation and Specific Recombination in Deoxyribonucleic Acids." Behind that formidable title was the kind of excitement that makes scientists glad they are scientists: in their studies of DNA, Marmur and Doty had probed close to the innermost secrets of life.

Potency Restored. Using breathtakingly delicate techniques, Marmur and Doty extracted solutions of DNA from bacteria and heated them to the boiling point for ten minutes. When a solution cooled quickly, it was found to have lost nearly all its biological potency. If cooled slowly, taking several hours to get back down to room temperature, 50% of the moribund DNA regained its activity. When it was applied to living bacteria, it changed their hereditary characteristics by a process called "transformation," which is considered a test for the potency of DNA.

In a long series of experiments, Marmur and Doty found out what had happened as they heated and cooled their DNA. When the solution neared the boiling point the twisted ropes of the DNA molecules untwisted, separated into single strands with no biological potency. In quickly cooled solutions, the strands stayed that way. But when the solution was cooled slowly, the separated strands had time to find each other, and twist together and regain much of their power to transform living bacteria.

Chemical Hybrids. The Marmur and Doty process has almost frightening possibilities for tinkering with life. DNA from related species of bacteria can be mixed together, and the strands can then be separated. When the solution is slowly cooled, the strands often join with partners of the other species, yielding chemical hybrids that can be used to transform bacteria into living, reproducing hybrids. By a similar process DNA can be created that will give such properties to bacteria as resistance to antibiotics. There is no theoretical reason why chemical hybridization cannot be applied to higher organisms, the highest of which is man.

The Marmur-Doty work was supported by the U.S. Public Health Service, which is, of course, vitally interested in anti-cancer research. Cancer is an excessive multiplication of human body cells, and any new knowledge about DNA, a key substance of cell division, is important in cancer research. But beyond such specifics, Marmur and Doty seemed to be approaching some answers to the mystery of life itself.

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