The Double Helix

Abstract

Crucial to the discovery of the double helix by James Watson and Francis Crick was, in the first place, their involvement with the spatial structure of DNA; what was the reason for their interest? At that time, the scientific world was still permeated with the notion that only proteins possessed the structural complexity necessary to develop countless alternative genetic characteristics (Fig. 5.1). Nevertheless, DNA was surely in some way associated with this genetic material, playing a still unknown important role in heredity, as, for example, the shaping of chromosome structure. That chromosomes were the seat of the genes was known since the beginning of the 20th century and that almost all cellular DNA was located in the chromosomes was shown, if not before, then definitively by Feulgen in 1923, with his eye-catching DNA-specific staining method (Feulgen & Rossenbeck, 1924). Yet, there was no compelling evidence for DNA alone being the carrier of hereditary information. Besides, no one had ever suggested that possibility, as such an assertion would obviously be wrong: the tobacco mosaic virus (TMV) was composed solely of 94% protein and 6% RNA, no DNA at all (Schramm & Dannenberg, 1944). However, even if the role of DNA in chromosomal heredity were an unspecific one, as, for example, simply holding the mysterious genes together, any assessment of this role still would represent an important new insight, and every contribution to its understanding would be welcome — even sensational!