HENRY M. SOBELL

CLOSING COMMENTS

It is apparent that understanding the mechanism of the intercalation of drugs and dyes into DNA (along with a large number of related topics) requires an interdisciplinary approach, combining information obtained from structural chemistry and molecular biology with concepts emerging from theoretical physics and nonlinear applied mathematics.

This branch of mathematical physics has quietly transformed the realm of science over the past quarter century, and there is every reason to believe that this will continue. A central concept has arisen in this area - the concept of emergent structures. These structures arise as a consequence of the ubiquitous presence of nonlinearity in nature.

Its real significance may be in the life sciences. The appearance of the premelton in DNA (signaling the onset of gene expression, chromosomal replication and genetic recombination) is one such example. Other more complex examples are the emergence of a tree from its seed, the development of a human being from its implanted fertilized ovum and, even, the origin of life on earth and the evolution of human consciousness.

Both physicists and biologists should recall the seminal discovery by Hodgkin and Huxley who showed that the conduction of a nerve impulse down the squid axon obeys the solution to a nonlinear partial differential equation, this being an example of nonlinear diffusion (A.L. Hodgkin and A.E. Huxley, J. Physiol. 117, 500-544 (1952)). The subject of nonlinear diffusion is closely related to soliton theory, and to the theory of emergent structures.

Is this just the "tip of the iceberg" that signals the entrance of physicists into biology in the quest to understand the PHYSICS of living processes?