44 



Cellular Structure and Activity 



the basis of real or supposed function and 

 composition (see Zollinger, '48a). Among 

 these are: storage granules, starvation gran- 

 ules, degeneration granules, resorption gran- 

 ules, glycogen granules, melanin and per- 

 haps the so-called "biosomes." 



Centrioles and Kinetosomes. These highly 

 important granules have not as yet been iso- 

 lated from fragmented cells. What little we 

 know about them rests mostly on circum- 

 stantial evidence based on cytological in- 

 vestigations. Being relatively large macro- 

 molecular aggregates they are doubtless very 

 complex chemically. Nothing approaching 

 a fractionation and chemical characteriza- 

 tion of these constituents has yet been at- 

 tempted. 



The centrioles and kinetosomes are pre- 

 sumably autonomous entities frequently 

 found in association with fibrous structures 

 (cilia, flagella, sperm tails, mitotic mech- 

 anism, trichocysts, etc.), and are thought to 

 be causally concerned with the production 

 and maintenance of the fibrous arrays. In 

 the ciliates much study has been given to 

 these granules, particularly by Lwoff ('50) 

 and Weisz ('51), from which it is concluded 

 that they are pluripotent morphogenetically 

 and essentially equipotential. Caspar! ('50) 

 considers them to be "visible plasmagenes"! 

 Though their relation to the genome and 

 cytogenes is far from clear, there seems little 

 doubt that these granvdes play a significant 

 role in processes of differentiation, particu- 

 larly of cortical structures of protozoa and 

 possibly of metazoan cells as well. Aside 

 from the problem of their role in differenti- 

 ation, the biochemical problem is at least 

 as interesting. If they do play a role in the 

 formation of organized protein fibers from 

 cytoplasmic precursors, one may expect that 

 enzymes may be involved. It may not be too 

 much to hope that sufficiently delicate mi- 

 cromethods may be developed by which 

 these structures may be isolated and studied 

 in vitro. 



SMALL GRANULE FRACTION 



(MICROSOMES) 



Claude's ('43) redefinition of the term 

 "microsome," which is an old one in cyto- 

 logical literature, would include any partic- 

 ulates that are separable from fragmented 

 cells at relatively high centrifugal force 

 (after removal of the heavier large granule 

 fraction). There is no doubt that this frac- 

 tion includes many types of particulates, the 

 composition of which may vary with growth, 



differentiation and function. Therefore, anal- 

 yses of the entire fraction cannot character- 

 ize any particular species in the particulate 

 population. However, such analyses indicate 

 something of the nature and possibly the 

 function of these components of protoplasm. 



According to Claude ('49, '50), micro- 

 somes have diameters in the range of 0.06 

 to 0.25^. They constitute some 15 to 20 per 

 cent of the dry weight of the cell and have 

 been shown to contain protein, lipid, ribose 

 nucleic acid (as much as 60 per cent of 

 that of the whole cell), some nucleotide and 

 a number of enzymes. It is thought that the 

 basophilic properties of cytoplasm may be 

 due primarily to the microsomes and to the 

 endoplasmic reticulum (which will be dis- 

 cussed below). At least five different sub- 

 fractions of the microsome fraction have 

 been obtained by differential centrifugation 

 (Chantrenne, '51, '52). The relative amounts 

 of UNA and other constituents vary with 

 the size of the particle, and Brachet ('50) 

 suggests that during embryogenesis the par- 

 ticles start out small but become more com- 

 plex and richer in RNA as development pro- 

 ceeds, this increasing complexity being an 

 important factor in differentiation. 



Several enzymes, including phosphatase 

 ATP-ase, dipeptidase and cathepsin have 

 been found to be associated with microsomes. 

 Notions as to the functions of microsomes 

 rest chiefly on circumstantial evidence. 

 Brachet ('49, '50) believes they may be con- 

 cerned with protein synthesis and discusses 

 their relation to plasmagenes and viruses. 

 Claude inclines to the view that they are 

 concerned with anaerobic respiration. Char- 

 gaff ('45, '49) isolated particulates 0.08 to 

 0.12yL(, in diameter from lung and other tis- 

 sue which have high thromboplastic activity 

 and he suggests that cell structuration may 

 be influenced by such intracellular enzyme- 

 containing particles (perhaps along the gen- 

 eral lines of the clotting process in blood). 



Basophilic Components. The basophilic 

 granules and filaments were early grouped 

 together under the term "chromidia" by 

 Hertwig. This term has been revived re- 

 cently by Monne ('48) and Lehmann and 

 Biss ('49) to denote the "self-duplicating" 

 RNA-containing submicroscopic particles 

 (biosomes) to which have been ascribed 

 most of the vital properties of protoplasm, 

 including respiration, metabolism, irritabil- 

 ity and morphogenesis! It is possible that 

 a portion of the chromidial apparatus is ac- 

 tually composed partly of adlineated micro- 

 somal particulates, as suggested by Bessis and 



