30 S. S. COHEN 



sopliisticated virologists prefer to avoid such experimental systems. However, 

 until the present, the role and relative independence of cell parts in such 

 matters as polymer synthesis has been explored most successfully in only a 

 few carefully chosen highly differentiated systems, which have not been of 

 experimental utility to virologists. The work of Brachet and Mazia with the 

 giant unicellular alga, Acetabularia, and with Amoeba, m which the metabolic 

 and particularly the synthetic capabiHties of nucleate and enucleate frag- 

 ments can be compared, emphasize this point. Nevertheless, experiments on 

 the relative independence of cell parts and function in these systems inevit- 

 ably raise the question, for example, of the necessity for a nucleus in the 

 synthesis of influenza and poliomyehtis viruses and point to the need of 

 developing new biological materials for the solution of such problems. 



Finally it may be asked whether, for example, our information on the 

 composition of the resting nucleus of an animal cell tells us anything about 

 a bacterial nucleus or even about the nucleus of a plant cell. Since but a 

 single paper (Spiegelman et al., 1958) bears on the composition of isolated 

 bacterial nuclei, and not many more exist which relate to the composition 

 of isolated plant nuclei, it is evident that extrapolation of one set of data to 

 other biological systems may be fraught with danger. 



Having noted a few of the important arguments agamst accepting any 

 generalized version of a cell, it is nevertheless convenient to present some 

 reference cell. A schematic representation of a parenchymatous cell of rat 

 liver, with currently available detail, is given in Fig. 3. As we shall see, a very 

 considerable portion of the analytical effort on cell structure and composition 

 has been directed at this unusual animal cell, which has been of httle interest 

 to the experimental virologist. 



We shall begin with a discussion of the chemistry of the nucleus, and con- 

 sider existing data on nuclear elements, such as chromosomes, nucleoli, 

 nuclear sap, and nuclear membrane. Data on cytojjlasmic components, such 

 as mitochondria and other particulates, and the cell sap will then be pre- 

 sented. Following the discussion of data on the comiDOsition of these cell 

 parts, we shall consider the problem of the locahzation of distribution of 

 metabolic function within cells, with particular reference to questions of the 

 localization and control of polymer synthesis, under normal and pathological 

 conditions of growth. Having presented the main relevant biological data, 

 we shall turn to the chemical problems of polymer syntheses which must be 

 answered within this biological context. 



B. The Composition of the Nucleus 



1. On the Existence of Chromosomes in the Interkinetic Nucleus 



As noted above, chemical work on nuclei has tended to concentrate on the 

 nuclei of adult tissues containing large proportions of interphase nuclei. 



