4 



Structure and Function 

 of the Nucleus 



The nucleus has received very much more attention since its discovery 

 by Robert Brown in 1835 than has any other part of the cell. While the 

 bulk of these investigations have been concerned with morphology, 

 particularly of the chromosomes in division, the development and use in 

 recent years of new cytological techniques for study of the nucleus have 

 contributed greatly to our knowledge of the biochemistry and physiology 

 of this cell structure. 



GENERAL MORPHOLOGY AND CHEMISTRY 



In general the nucleus tends to be spherical, but may be fusiform, 

 ellipsoidal, flattened, or irregular, depending to some extent on cell shape 

 and function. Its size tends to bear a constant relation to the cytoplasmic 

 volume (O. Hertwig, 1906), but there are many exceptions. In young 

 cells it is more often spherical and centrally located, but in differentiated 

 ones it may be displaced and irregular in shape. 



The interphase nucleus (a nucleus not in the process of active divi- 

 sion) consists of (1) a nuclear envelope surrounding (2) a nonstaining 

 or slightly chromophilic mass, the nucleoplasm, in which are dispersed 

 (3) the chromosomes, which are considered to be nucleoprotein struc- 

 tures, (4) the chromocenters, and (5) one or more basophilic bodies 

 called nucleoli. The following discussion is concerned with the structure 

 and chemical makeup of the several parts (Figure 4-1). 



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