STRUCTUKAL AND CHEMICAL ARCHITECTURE OF HOST CELLS 57 



to distilled water. In tins medium, a mitochondrion may swell to more than 

 5 times its normal volume before bursting. The stretching of the membrane in 

 itself appears to facilitate release of internal metaboHtes, previously 

 nondiffusible. 



The integrity of the membrane may be preserved by isolation in the 

 presence of hypertonic sucrose. During experimentation in isotonic media, 

 the preservation of the membrane requires an energy source, such as added 

 ATP or UTP (uriduie triphosphate) (Lehninger, 1956). The particles will 

 concentrate Na+ and K+ without swelling under conditions in which ATP 

 is being generated (Macfarlane and Spencer, 1953). Various aspects of the 

 movement of water and ions in mitochondria have been discussed by 

 Lehninger (1956), Price, C. A., et al. (1956), and Fonnesu and Davies 

 (1956). 



The largest number of studies in cell fractionation has been effected 

 with animal tissues. Although particles bearing enzyme activities have 

 been isolated from homogenates of plant tissues, in most early studies 

 their appearance was no longer comparable with the structures visible 

 within the cell. In recent studies (Martin and Morton, 1956; Hodge 

 et al., 1957), as a result of efforts to preserve the surface membranes, 

 plant mitochondria have been isolated whose morphological and enzymatic 

 properties are comparable to mitochondria observed in sections of 

 plant cells and which resemble the isolated mitochondria of animal 

 tissue. 



As will be seen below, mitochondria fulfill the role of a powerhouse for the 

 ceE, storing the energy derived from respiration and dehydrogenations in 

 compounds such as ATP or thioesters, which are capable of supporting 

 the performance of work. In addition, the special requirements of differen- 

 tiated cells result in the differentiation and specialization of mitochondria. 

 For example, the striated flight muscles of certain adult insects contain 

 large spherical intrasarcoplasmic bodies called sarcosomes (Watanabe and 

 Wilhams, 1953). These are arranged in rows along the fibril and constitute 

 about one-third of the total muscle mass. Sarcosomes are really differentiated 

 mitochondria in which the supply of chemically stored energy is integrated 

 wdth the functional demand of the muscle fiber. In Drosophila their size 

 is independent of the ploidy of the cell; it is estimated that in this 

 organism their ENA content is less than 5 % (Eudkin and Schultz, 

 1956). 



The accumulation of foreign substances is effected very actively by the 

 mitochondria of kidney tubules (Zollinger, 1950a). According to this worker, 

 proteins are taken up to form droplets, which coalesce within the mito- 

 chondrial core. Eventually, the membrane degenerates and the mitochondrion 

 becomes a drop of secretion. It is postulated that a similar process occurs in 



