The Revolution in Biology

In its impact on biology, the discovery of the DNA structure in 1953 by Watson and Crick is rivaled only by Darwin’s and Wallace’s ideas on evolution and by Mendel’s discovery of the basic laws of heredity. It opened up the possibility of understanding the chemical basis of heredity, by showing that DNA (deoxyribonucleic acid), the fundamental chemical substance of which genes (a chromosome is a linear collection of genes) are composed, had a simple, well-defined three-dimensional structure eminently suited to its hereditary role.
Until the dramatic announcement of the doublehelical structure of DNA, there was complete ignorance of how a chemical substance could carry out the multifold activities needed for a genetic substance. Particularly mysterious was the problem of the self-duplication of the gene. Every time a cell divides to produce two new cells, its chromosomes also divide, producing two gene sets identical in structure to the pre-existing set. But until the structure of the gene became known, there was no way of even formulating the problem. And since DNA was thought to be very complicated, there was fear not only that the structure would not be solved for many decades, but also that when DNA was finally deciphered, it would be so subtle that few scientists would be able to understand it completely.
Hence the extraordinary excitement among the world’s biologists when Watson and Crick showed that the basic features of DNA were straightforward and led immediately to a highly plausible model for how one DNA molecule could be duplicated to form two identical copies. The way in which genes duplicate is a concept not restricted to the very fewit is of such simplicity that now it is routinely explained to virtually all students of high school biology.
A revolution in biology was thus set in motion which in many ways parallels the explosive development of atomic physics following Bohr’s 1912 analysis of the hydrogen atom and the subsequentelaboration of quantum mechanics, upon which the development of atomic energy depended. The most striking consequence of this biological revolution has been the virtually complete working out of the genetic code. Given the structure of DNA, it became possible to ask how it can convey genetic information. This was shown to be through the sequence of the four different nucleotides in a DNA molecule. Each different gene has a different nucleotide sequence. A genetic message can thus be visualized as a very long word written in a four-letter alphabet. This message is then translated, by a cell’s proteinsynthesizing machinery, into the specific sequence of amino acids which characterizes a specific protein.
We know that each gene (that is, a collection of nucleotides) serves as a mold for the synthesis of a specific ribonucleic-acid molecule (RNA), which itself also serves as a mold, in this case to order the amino acids during the construction of a protein molecule. Moreover, it is further known that groups of three nucleotides within each RNA molecule specify a given amino acid and that in virtually all cases, the exact nucleotide sequences corresponding to each amino acid can be determined.
Directly leading from this work is an increasing understanding of why some genes work faster than others, In the near future, we should have a real insight into the chemical basis of embryological development and an understanding of the molecular basis of many important diseases. Already most striking is the abrupt change from the pre-war period when viruses were totally mysterious objects: today they are seen as well-defined molecular assemblages whose multiplication processes are known in great detail. It is hoped that this past decade’s successful assault on the nature of viruses will soon be followed by the discovery of how viruses can transform normal cells into cancer cells, an understanding that may lead to the control of many malignant diseases.
The Editor