Unusual Hydrogen Bonding Patterns and the Role of the Backbone in Nucleic Acid Information Transfer

Why was this? Culture plays a role in science, as it does in other human activities. Culture is defined by what we accept without explanation, what demands an explanation, and what is “aesthetic”. The rapid acceptance of the “elegant” Watson−Crick model can be attributed to the culture of the time. How so? As it turned out, the regularly sized “rungs” on the two strand duplex ladder fit closely the then-cultural expectation of what a genetic molecule should look like. These expectations came from a book entitled “What is Life?” Published a decade earlier by Erwin Schrödinger, the book began by noting the thermodynamic “impossibility” of transmitting information at the level at which information was, apparently, transferred by living systems. Schrödinger proposed to resolve this apparent paradox with a genetic polymer that formed an “aperiodic crystal”. Here, the overall shape and size of the different information storing units (Schrödinger did not say what they would be) would be the same, so that interchanging the informational bits did not change the overall geometry of the genetic structure. Watson and Crick immediately recognized that their double helix met Schrödinger’s requirement. The size complementarity of the Watson−Crick pair (large purines pair with small pyrimidines) allows information to change without the size of the coding unit changing. This allows the double helix to have the structural features of Schrödinger’s aperiodic crystal. The pattern of hydrogen bonding units on the Watson−Crick edge of the nucleobase then ensures that the correct big component finds its small partner. This was the first reason that the double helix was accepted with little supporting experimental evidence. Second was the “elegance” by which the double helix explained genetic replication. All that was necessary was to separate the two strands, and then allow each strand to