28 S. S. COHEN 



products of the variegation of chloroplasts, even as proposed by Woods and 

 Dubuy (1943). Also, we would wish, to know which viruses, if any, have been 

 produced by mutations in the production of microsomes. As is weU known, 

 many carcinogenic treatments are also mutagenic, and it is important to 

 know whether tumor viruses, as well as tumor cells, may not arise as the 

 result of such treatments. 



As is evident from this discussion, problems of virus origin, specificity, and 

 multiplication have merged with current problems of cytology, development, 

 and genetics and the dissection of mechanisms of inheritance. AD of these 

 problems have begun to be formulated in common terms. Fortunately, the 

 biochemistry of polymer synthesis also cuts across aU of these fields. Bio- 

 chemical development in this particular area has also kept pace with know- 

 ledge in these biological disciplines and has even begun to contribute signi- 

 cantly to the advancement of biological knowledge. With this realization, we 

 shall discuss the basic data of these biological disciplines, particularly as they 

 relate to biochemical problems of polymer formation, in the hope and ex- 

 pectation that the emerging principles and problems of cellular biochemistry 

 will be of fundamental interest and utihty in the development of knowledge 

 concerning the viruses. 



II. Cellular Organization 

 A. On the Cell in General 



The development of a biochemical cytology, as well as an increasing 

 sophistication of the biochemist with respect to biological phenomena, have 

 emphasized the facts and problems of cellular organization. That cells are 

 not mere bags of enzymes dissolved in a soup or jellied consomme of meta- 

 bolites has come to be accepted not only by biologically oriented biochemists 

 but by the classic enzymologists as well. This is marked by the development 

 of a literature in which it is no longer sufiicient to report that an enzyme has 

 been obtained in ceU-free preparation, but also that it sediments as a particle 

 of large particle weight or, alternatively, is "soluble," i.e., not readily sedi- 

 mentable. In dealing with cells, numerous investigators will also attempt to 

 determine if an enzyme is not present in a nuclear fraction or in one of several 

 separable cytoplasmic fractions, and even if its apparent cellular distribution 

 is not related to its apparent function. Thus, biochemical cytology is rapidly 

 accumulating data on the locaHzation of enzymes and on the metabolic 

 division of labor. 



However, in the increasing activity of biochemists to fractionate the cell, 

 this atom of the biological world is frequently treated as an invariant unit 

 of structure. Few biochemists appear to take into account the fact that the 



