The Duplication Mechanism of Deoxyribonucleic Acid

Abstract

RECENT investigations have shown it to be more and more probable that genes are deoxyribonucleic acid molecules. Furthermore, Watson and Crick¹ have given strong arguments for assuming that these molecules consist of two polynucleotide chains wound helically in a large number of turns around a common axis and tied together by hydrogen bonds between pairs of corresponding purines and pyrimidines, so that adenine can pair only with thymine and guanine only with cytosine. In order to explain the duplication process of the deoxyribonucleic acid molecule, Watson and Crick have suggested that the two polynucleotide chains may be separated and each chain catalyses the synthesis of a complementary chain. The difficulty in this process is the separation of the two parallel helices which are highly intertwined and locked together by a large number of hydrogen bonds, the breakage of all of which would need a large amount of energy. To overcome this difficulty, Delbrück² has suggested a somewhat different mechanism, whereby the two chains are separated and later re-combined by a series of breaks and reunions in a zipper-like fashion. However, this mechanism also seems both too complicated and somewhat improbable since, for example, all these breakings of bonds would again need a considerable amount of energy.