SPECIFICITY OF LONDON-EISENSCHITZ-WANG FORCE 53 



the assembly process might either be broken up or will simply stop growing 

 because they will correspond to a structure which cannot be fitted together 

 any further. A set of a few constituent molecules properly fitted and bonded 

 together will again be specifically attracted and oriented by its counterpart in 

 the original unit. 



(a) In the case of a long DNA helix, self-duplication might perhaps come 

 about as follows. The surrounding medium supplies polynucleotides. Brownian 

 motion and specific London attraction provide for a mantle of nucleotide pairs, 

 selected to correspond to the nucleotide pairs of the parent helix, to be laid 

 around this original helix. The London force causes a particular orientation of 

 each daughter nucleotide pair in the mantle with reference to its corresponding 

 parent nucleotide pair. This mutual orientation can be described as follows. 

 Draw a radial line from the parent helix axis through the center of that parent 

 nucleotide pair; the daughter nucleotide pair can be generated by performing 

 a 180° screw translation outwards along this line which puts the parent pair 

 over into the daughter pair, located in the mantle. As the circumference of the 

 mantle is larger than that of the parent DNA double helix, the regularly ar- 

 ranged daughter pentose-phosphate groups are separated by some gaps from 

 neighbor groups along the helixes. The formation of the DNA replica may then 

 occur by the closure of some gaps, and finally all of them, accompanied by ionic 

 concentration changes in the medium, permitting the daughter helix sections 

 to peel off from the parent helix. Such a daughter helix then has the same 

 pentose-phosphate helices and the same secjuence of base pairs as the parent 

 helix; however, each base pair is flipped 180° around its radial line, compared 

 with the orientation of the parent helix pair. This replica is therefore a 'flip 

 conjugate' of the parent DNA; the next generation is expected to be again like 

 the original. 



Biological specificities occur in many other connections (Rabinowitch, 1941) 

 where it is not always the case that the participating molecules possess as out- 

 standing a stability as the genes do, and where the specific interactions involve 

 non-identical molecules. It would be premature to speculate as to the signifi- 

 cance of the above calculations in regard to the wider field of biological spec- 

 ificities. It is clear that complementarity, favored because of electrostatic or 

 because of general van der Waals stabilization, plays a most important role not 

 only in deciding molecular structure, but also in determining intermolecular 

 interaction (Pauling, 1940, 1948, 1957; Pauling, Campbell and Pressman, 

 1943; Campbell, 1957). 



An interesting effect of high specificity may, however, come up in the fol- 

 lowing fashion. For simplicity of explanation, this effect will be illustrated in 

 terms of two identical protein helixes which possess occasional big side groups. 

 Let the helixes be alongside each other, with their axes vertical, one helix being 

 a little displaced (in the direction of the helix axes, i.e. elevated) with respect 

 to the other, and let the helixes be turned around their axes such that some of 



