76 The Structure of Protoplasm 



around the particle as a whole. The strength of attachment will 

 depend to such a great extent upon the specific nature of the 

 approaching atoms and faces that little more can be said than that a 

 considerable although a relatively limited number of variations 

 occur. This must be evident when one considers the possibilities 

 existent in the approach, face to face, of two protein particles. An 

 H-bridge may be effective at one point, several ions may pair up at 

 other points, and van der Waals' forces will always be effective 

 when the surfaces are close together; that is, within 3 to 5 A. 



Attachment of prosthetic groups to the protein is thought to 

 occur specifically. In some instances the small molecule may be 

 bound directly to the protein through hydrogen bridges, in other 

 cases through ionic pairing. Primary valence bonds and even van der 

 Waals' forces are not to be excluded. The spacing between the 

 atomic constituents which are thought to be active in the attach- 

 ment of the prosthetic group to the protein was shown to be com- 

 patible in certain instances with the distance of about 7 A between 

 adjacent residues on the protein chain. 



These fundamental concepts of molecular models and inter- 

 molecular forces of attraction make it possible to determine the 

 nature of larger structures. The larger structures we may think of 

 as particles at one moment, principally because we are familiar with 

 microscopic particles in protoplasm; while at another moment we 

 may think of them as mechanisms, because we know from experi- 

 mental procedures that particles are involved in activities of various 

 sorts. From the composition of the particles we are enabled to 

 carry over the structural molecular concepts to the mechanisms, 

 but only insofar as we know the composition of the mechanisms. 



Organization of these mechanisms, in some as yet undetermined 



manner, in the cell, we assume at the present stage of investigations, 



constitutes the physical basis for vital activities. In conclusion, we 



feel that this organization within the cell, which is without doubt 



responsible for the phenomena presented by a living organism, is 



of such a nature that further elucidation of it may come from the 



application of the fundamental concepts mentioned, to experimental 



investigations involving both biological and physical-chemical pro- 



2edures. 



LITERATURE CITED 



1. Sponsler, O. L. The Quarterly Review of Biology VIII, 1, 1933. 



2. Gaidukov. N. Ber. d. Deutschen Bat. Gesell 24, 107, 155, 580. 1906; Dunkel- 



jeldheleuchtujig und Ultraynicroscopie in der Biologie und in der Medi- 

 zin, Jena. 1910. 



