Molecular Interactions and Structure 

 Formation in Biological Systems 



David F. Waugh ^ 



The three-dimensional display of structural complexity in cells 

 and tissues, now so convincingly visible in the evidence from elec- 

 tron microscopy, is at the colloidal level, thus the level where one or 

 two dimensions of the particles (rodlets, lamellae) which result 

 from molecular interaction are near the dimensions of the interact- 

 ing molecules themselves. We accept the fact that the functional 

 aspects of cells, tissues, organs, etc., must be a natural (thermo- 

 dynamically acceptable) result of the organization at the level 

 mentioned, and, although we are not in a position to state the type 

 or extent of knowledge which will be necessary to understand the 

 way in which subcellular colloidal aggregates modify each other's 

 activities to produce the net result of "life," several aspects of in- 

 teraction have been examined in a way which must excite all in- 

 terested in biological processes. These I have been asked to discuss 

 briefly. 



Manipulation and interaction at the molecular level involve 

 selections of the interacting molecules; thus, the interactions are 

 specific. We are familiar with the high degree of specificity ex- 

 hibited by enzyme-substrate interactions ( Wilson, 1959 ) , in energy 

 transfer (Lehninger, 1959), in immunological interactions (Land- 

 steiner, 1945), in the formation of tissues such as collagen and 

 elastin (Schmitt, 1959), in the formation of organs, and during the 

 course of embryonic development, to cite a spectrum of examples. 

 As we shall see, specificity of interaction between molecules coming 

 into close contact may be understood on the basis of short-range 

 interactions between appropriately placed submolecular groups of 

 atonijS having different interaction characteristics. Catalyzed chem- 



^ Massachusetts Institute of Technology, Cambridge, Massachusetts. 



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