CHAPTER 20 



Nucleic Acids in Chromosomes and Mitotic Division 

 BO THORELL 



Page 



I. Introduction 181 



II. The Chromosomal Nucleic Acids 182 



1. Analyses of Isolated Chromosomes 182 



2. Analyses of Chromosomes in situ 185 



a. The Feulgen Reaction 185 



b. Staining Methods 186 



c. Radiation Absorption Measurements 188 



III. Changes in the Chromosomal Nucleic Acids During the Cell Cycle 192 



1 . Quantitative Changes " 192 



2. Turnover Studies 196 



IV. Concluding Remarks 198 



I. Introduction 



Reproduction in the cell is in general effected by division in which the 

 essential process involves an equal distribution of the hereditary material 

 between the daughter cells. The hereditary material (the genes), which 

 forms the basis of cellular development and function, is in higher organisms 

 mainly located to the nucleus of the cell. Nuclear division may thus be 

 regarded as the characteristic process during cellular reproduction. 



The ordinary mechanism of nuclear division is mitosis, in which the 

 nucleus is transformed into longitudinally split chromosomes. The longi- 

 tudinal halves are then distributed equally between the two daughter nuclei 

 by a special mechanism, the spindle. This is formed at the beginning of 

 mitosis in connection with the centriole bodies in the cytoplasm. 



The chromosomes in the original sense (Flemming, Hertwig, Weissman, 

 and others (1875-81) refer to the condensed, stainable nuclear material 

 during mitosis. 



During the stage between two successive divisions (interphase), most of 

 the chromosomal material is dissolved into elementary structural units, 

 also called the chromatin threads (chromonemata) . In this state the nuclear 

 material is believed to be able to perform its manifold physiological func- 

 tions. 



This activity seems to cease as soon as the formation of the mitotic 



181 



