King of Codes
Scientists marvel over DNA's structure and coding, even as they puzzle why it seems to never change.
“Ode to the Code” by Brian Hayes, in American Scientist (Nov.–Dec. 2004), P.O. Box 13975, 99 Alexander Dr., Research Triangle Park, N.C. 27709–3975.
It’s been four decades since life’s genetic code was cracked, yet a nagging question remains: Why does this particular system for communicating vital chemical instructions govern virtually all life on Earth? Shouldn’t there have been significant variations in the code as it naturally occurred in life, thus making it, like all living things, subject to evolution over time?
Consider ribonucleic acid (RNA), which often carries instructions to cells telling them how to assemble amino acids into a specific protein. The RNA language uses an alphabet of four “ to make 64 three-s still an astronomical number (1083, to be precise) of ways the instructions could be coded. Why this one?
Francis Crick, co-discoverer of the double helix structure of DNA, argued that the code may have been a “frozen accident,” becoming so deeply embedded in the core machinery of life at some point in the distant past that any further change became impossible, notes Hayes, a senior writer for American Scientist.
Resisting that theory, some scientists have pointed to “certain protozoa, bacteria and intracellular organelles [that] employ genetic codes slightly different from the standard one.” But nobody can find any adaptive advantage in those variants.
Other researchers argue that the code as it exists is already close to perfect. Its most evident virtue: its apparent ability to minimize errors in the transmission of genetic information. For example, the way the code is set up—so that some of the 64 codons are “synonyms” for others, with the synonyms physically clustered together—ensures that, even when an error occurs, the proper amino acids are often assembled. Computer simulations with up to a million random codes have shown the existing code to be “a stellar performer” in minimizing errors—“the best of all possible codes,” as one team of researchers put it several years ago.
But the case is not entirely closed. The computer simulations have certain weaknesses, and scientists continue to speculate about the code. Some are intrigued by various mathematical patterns in the code—such as the fact that the number 64 is equal to both 43 and 26. The patterns suggest many possibilities, including, unlikely as it may seem, connections with the I Ching.