Inside the Cell 



49 



From these experiments we leam that the constituents of the 

 cytoplasm are not all mixed up, but arranged in particles or struc- 

 tures of different kinds. Much work has been done to explore the 

 functions of these particles. It has been found that the mitochondria 

 contain the oxidizing enzymes of the cells. They are in fact the power 

 houses of the cells. The electron microscope has shown them to 

 possess an internal structure of membranes, by means of which the 

 enzyme processes are controlled and organized, but their detailed 

 constitution is still unknown. 



/ Contents of 

 this sector ^ 



I 



I are magnifiedy 



Microsomal filaments 

 with submicrosomes 

 (black dots) attached 



f • 



Fat globule 



Mitochondrion 



Nucleolus 



-Nucleus 



FIG. 12. Diagram showing some of the structures usually present 

 in a cell 



Mitochondria are relatively large bodies. A typical one is about 2// 

 long and \ jx wide (1 /x = 1 / 1000 of a millimetre) and contains about 

 a milHon protein molecules of typical size. They appear in the elec- 

 tron microscope pictures (see m, Plate 7) to be crossed by thin 

 membranes arranged in pairs. It would seem that the enzymes are 

 organized on these membranes. A considerable number of enzymes 

 is present in a single mitochondrion, to bring about the many chemical 

 changes necessary, but even if there were five hundred distinct 

 enzymes, it would still be possible to have a large number of molecules 

 of each. 



D 



