"Do We Have the Structure of DNA Right?" by Robert Root-Bernstein, in Art Journal (Spring 1996), College Art Assn., 275 Seventh Ave., New York, N.Y. 10001.

The double helix of DNA (deoxyribonucleic acid) is one of the icons of the modern age. What most textbooks do not reveal, says Root-Bernstein, a professor of physiology at Michigan State University, is the real possibility that this is not the structure of DNA.

Biologists James Watson and Francis Crick proposed the double helix (with two chains twining around each other, connected by "steps" formed by pairs of nucleic-acid bases) as the structure in 1953, and later won the Nobel Prize for their work. Most features of their proposal—including the base-pairing idea, which is the basis for how information is encoded in genes—have been verified many times since. However, the famous double-helix model remains "a bit doubtful," Root-Bernstein says.

A big problem is that it is not clear how a DNA double helix is unwound so as to allow it to be replicated. Unwinding the DNA

strands within the cell nucleus, Root-Bernstein says, would be like unwinding several hundred kilometers of twisted strands with the thickness of fishing line, inside a basketball: "Where does the energy come from to perform the unwinding of the strands? What mechanism can be imagined that could perform such a feat, even if the energy were available to do it?"

Watson and Crick themselves recognized in 1953 that the unwinding problem was "formidable," and they noted a possible alternative to the double helix: a "ribbonlike" or "sideby-side" structure, in which the two chains were joined together by the base pairs but did not twist about each other. But the double helix, Root-Bernstein says, had an aesthetic appeal for the two scientists that the ribbon-like alternative did not. As Watson himself often said, the double helix "was too pretty not to be true."

Nevertheless, it may not be true, as some scientists have argued since the 1970s. Most researchers, however, cling to the double helix, avoiding the unwinding problems, Root-Bernstein says, by asserting "that the strands are repeatedly broken and reattached way of sidestepping the problems with the by enzymes during the replication process." double helix, he observes, but they hardly Such mechanisms may be nature’s ad hoc enhance its aesthetic appeal.