280 UNITY AND DIVERSITY IN BIOCHEMISTRY 



The nucleus contains a number of other phosphorylated derivatives and 

 inorganic elements such a K, Ca and Mg. 



When mitosis occurs, the chromatin filaments combine into chromo- 

 somes which divide longitudinally and then distribute themselves between 

 the two halves of the cell. This process is aided by the aster, a structure 

 formed at the beginning of mitosis and surrounding the centrosome. It has 

 been isolated from sea urchin eggs and shown to be protein in nature. 



The nucleus is lacking in a number of important enzymes for cellular 

 oxidation such as cytochrome oxidase, succinic dehydrogenase, uricase, 

 D-amino acid oxidase, etc., and so respiration does not occur. However, it 

 does contain a glycolytic system, although of low activity. In the nucleus 

 is concentrated a system of enzymes for the synthesis of nucleic acids and 

 nucleotides. It is found that radioactive phosphorus is always incorporated 

 more rapidly into the RNA of the nucleus than into the RNA of the cyto- 

 plasm. So, there is little doubt that the nucleus contains enzyme systems 

 for the synthesis of the two types of nucleic acid. 



D. Conclusions 



It is true that the study of the distribution of enzymes in the cell has only 

 just begun, nevertheless they have brought to our notice several important 

 facts concerning cellular metabolism. From these studies we see that 

 the cytoplasm is the principal region for the performance of anaerobic 

 degradations which provide the mitochondrial machine with fatty acids, 

 amino acids, and pyruvic acid. Since most of the glycolysis occurs in it, 

 the cytoplasm is manufacturing energy-rich bonds by an anaerobic pathway. 

 In addition the cytoplasm, or more particularly the microsomes, appears 

 to be the home of protein synthesis. 



In the mitochondria is localized the respiratory part of the priming 

 reactions, the fatty acid cycle and the tricarboxylic acid cycle, the chief 

 providers of the ATP required for cellular work. However it appears that 

 the transfer of electrons from DPNH or TPNH to cytochrome-c can also 

 take place apart from the mitochondria. 



With its enzymes for the synthesis of nucleosides and nucleoproteins, 

 the nucleus appears to be the repository of the specific DNA structure 

 and the apparatus for its transmission. It also has a part to play in the 

 control of the synthesis of the cytoplasmic nucleotides and of protein 

 synthesis in the cytoplasm. Whether the latter is controlled through the 

 synthesis of the microsomes or otherwise, the part played by the nucleus 

 has been demonstrated on numerous occasions although the mechanism 

 still remains to be discovered. 



REFERENCES 



Allfrey, V. G., MiRSKY, A. E. and Stern, H. (1955). The chemistry of the cell 

 nucleus. Advanc. EnzymoL, 16, 411-500. 



