Happy Anniversary: Fifty Years after Watson and Crick's Insight, Scientists Continue to Take a Close Look at DNA's Double Helix

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On April 25, 1953, a brief research paper appeared in the British scientific journal Nature. Fifty years later, it's one of the most famous publications of all time and often considered the start of the molecular biology and genetics revolution that continues today. In that report, two young scientists at Cavendish Laboratory in Cambridge, England, proposed what they called a "radically different" structure for DNA, the material that scientists of the time had recently concluded stored an organism's genetic information. The pair argued that the DNA molecule resembles a spiral staircase. In the proposed arrangement, two strands are twisted together and connected at each step by a pair of so-called chemical bases, one jutting off each strand.

Such a structure hinted at the solution to another major riddle of biology: how a dividing cell copies its DNA so each daughter cell gets identical genetic information. The two strands could simply unwind, separate, and each make a new opposing strand according to the string of chemical bases it carries.

"It has not escaped our attention that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material," noted James D. Watson and Francis H.C. Crick.

On the eve of the 50th anniversary of the double helix's grand debut, Science News presents a gallery of images depicting the DNA molecule and, in one case, the genetic information it encodes.

FIRST LOOK (above, inset) The historic X-ray image of DNA taken by Rosalind Franklin of King's College in London in 1952. Though supplied to Watson and Crick without Franklin's knowledge, the image was an important clue to DNA's molecular arrangement as a double helix. The 1953 photograph (above) shows Watson (left) and Crick posing with one of their original models of DNA.

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SURFACE TRACE (left) In the late 1980s, researchers began to study DNA with a scanning tunneling microscope (STM). In this method, a sharp tip establishes an electric current between it and a target below that depends on the distance between them. By moving to maintain a steady current, the STM's tip can map an object's surface. In this false-color image, the DNA double helix is evident as the diagonal ridge of orange mounds. Scientists had hoped that STM imaging could distinguish among DNA's four bases so it could give a direct reading of the sequence of bases on a DNA strand, but the technique's resolution wasn't good enough.

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SPECIAL SITES (below) The fine metallic point of an atomic force microscope (AFM) directly traces the surfaces of microscopic objects. This 1997 picture, taken by researchers at Oak Ridge (Tenn. …