The Nature of the Forces Operating in the 



Process of the Duphcation of Molecules 



in Living Organisms 



LINUS PAULING 



California Institute of Technology, Pasadena, Calif., U.S.A. 



Each form of life has the power of manufacturing molecules characteristic of 

 that form. A human being manufactures kinds of molecules, including probably 

 some tens of thousands of different kinds of proteins, which are characteristic 

 of him. He passes on to his child the power of manufacturing many of the same 

 molecules. A virus particle, with the collaboration of a suitable host, may have 

 as immediate progeny hundreds or thousands of virus particles that are made in 

 its own image. 



It may be that hfe originated on Earth when, in the 'hot, thin soup' containing 

 thousands and thousands of different kinds of molecules that had been formed 

 by more or less random chemical reactions, there was, by chance, formed a 

 molecule with the power of catalysing the synthesis of rephcas of itself. 



Whatever the details of the process of duplication are, it is characteristic of 

 hving organisms that they contain molecules with the power of manufacturing 

 dupHcates of themselves. A human being has molecules of haemoglobin in his 

 red cells; his children have molecules of haemoglobin in their red cells, usually 

 identical with those in the red cells of the parent. A human being has molecules 

 of deoxyribonucleic acid in the nuclei of his cells ; his children have molecules 

 of deoxyribonucleic acid in the nuclei of their cells ; and it is believed that many 

 of these molecules are identical in structure with those of the parent. 



In order to understand the nature of life and the origin of hfe we need to know 

 what the process is by which molecules are able to dupHcate themselves, what 

 the forces are that are operating during the process. 



It is my belief that the process of duplication of molecules and the other 

 processes that show biological specificity involve not only the interatomic forces 

 comprised under the name of chemical bonds but also the weak forces that oper- 

 ate between atoms — the forces of van der Waals attraction, electrostatic attraction 

 between charged groups, and the formation of hydrogen bonds; and that in 

 general biological specificity is the result of the especially strong interaction, 

 involving collaboration of these weak forces, that can occur between molecules 

 that are complementary in structure. It is this thesis that will be presented in 

 the following paragraphs. 



Let us ask how a molecule A, which we may call a gene, could produce a 

 replica of itself. One conceivable way is that some special stabiHzing force of 

 interaction occurs between two identical molecules, A and A, such that one 



215 



