Using wire models, intuition, a limited knowledge of chemistry and trial-and-error methods, Researchers James Watson and Francis Crick determined that the heredity-transmitting DNA molecule is shaped like a spiral staircase. Al though they had no way of taking a firsthand look at their discovery, they managed to deduce a detailed description of the now famous “double helix” that paved the way for the new science of molecular biology and won them the Nobel Prize. For all the work that has been done in the field since Watson and Crick made their pioneering studies in 1953, no one had been able to display any hard and fast visual evidence to confirm the spiral structure of DNA. Now that evidence is in. A young California scientist reported to a Los Angeles meeting of the Biophysical Society last month that he had succeeded in photographing a DNA molecule.
When he set out to take his DNA pictures, Caltech Graduate Student Jack Griffith, 26, was well aware that his task would be extremely difficult. The DNA molecules from the pea-plant chromosomes used in his research project were only one thirteen-millionth of an inch across and would be agonizingly difficult to distinguish even with the aid of the most powerful electron microscope. In addition, the molecules would be distorted or destroyed by the instrument’s electron beam before they could be photographed. Then how could they be photographed at all?
After two years of failure, Griffith finally found an answer. Using a delicate technique that he describes as “more witchcraft than science,” he began spraying his DNA samples with a thin coating of tungsten atoms. The tungsten film enhanced the outline of the complex molecule and was heavy enough to shield it from the electron beam. But it was not so thick as to obscure the molecular structure. The resulting pictures, which Biophysicist Griffith painstakingly developed himself to bring out maximum detail, show a blurred image that has been magnified 7,300,000 times. Fuzzy as they are, the pictures are clear enough to reveal two DNA strands that are coiled and intertwined in a double helix—just as Watson and Crick predicted nearly 16 years earlier.
More Must-Reads from TIME
- L.A. Fires Show Reality of 1.5°C of Warming
- How Canada Fell Out of Love With Trudeau
- Trump Is Treating the Globe Like a Monopoly Board
- Bad Bunny On Heartbreak and New Album
- 10 Boundaries Therapists Want You to Set in the New Year
- The Motivational Trick That Makes You Exercise Harder
- Nicole Kidman Is a Pure Pleasure to Watch in Babygirl
- Column: Jimmy Carter’s Global Legacy Was Moral Clarity
Contact us at letters@time.com