MOLECULAK STRITCTUHK IN I'KOTOI'I.ASM 



183 



pointing' tuwarils a molecule of succinic acid 

 (B). In Fig. 9 the same two residues are 

 in close contact with the glucose inolecule. 

 In Fig. 10 the active points of attachment 

 of lactoflavinphosphate (Theoi-ell 1937) on 









^* 



•^ 



B 



Fig. S. Eeiiroduction of models to show similarity 

 of spacing, about 7 A, which may exist between the 

 active groups of succinic acid B and the terminal 

 groups of the two residues arginine and tyrosine 

 on the protein chain, A. 



the right are shown in close approach to the 

 same two residues as in the preceding fig- 

 ures. Finally in Fig. 11 the spatial cor- 

 respondence is shown between these two 



Tig. 9. Reproduction similar to that of Fig. 8 

 except that the prosthetic group at B is glucose. 



residues and the ])robable active groups of 

 lecithin. There is no significance in the 

 choice of arginine and tyrosine; the dis- 

 tance, 7.0 A, is pi-actically the same regard- 

 less of the kind of i-esidues chosen. 



These substances, the prosthetic groups 

 attached to the protein particles, represent, 

 however, a relatively small fraction of the 

 materials which may occur in the water 

 channels. They are included principally in 

 the 2 per cent which was assigned to "other 

 organic and inorganic substances," while 

 1 per cent was considered as a minimum for 

 fatty molecules, 7 per cent for protein, and 

 90 per cent for water. 



We turn our attention to the water chan- 

 nels which were represented on our en- 

 larged scale by the layers of sand in our 

 9-foot room. When we assume that most 

 of the organic and inorganic substances 

 occur in these channels, it becomes evident 

 tliat narrow channels might easily become 

 blocked with excess materials. The 3 per 

 cent which we have allotted to three types 

 of substances — to fatty materials, other or- 

 ganic compounds and inorganic substances 

 — if apportioned about 1 per cent each will 

 supply for every single protein molecule of 

 36,000 molecular weight about 5 fatty 

 molecules similar to lecithin, 25 organic 

 molecules of the size of a hexose sugar and 

 about 50 ions like NO3. These molecules, 

 large and small, are numerous enough when 

 hydrated to prevent ready diffusion unless 

 the proteins form aggregates of a dozen or 

 more of the 36,000 size. 



I wish at this point to indulge in some 

 wild speculation which, however, may not 

 be excessively wild when examined more 

 closely. I wish to suggest a picture for 

 cytoplasm based upon these molecular and 

 submicroscopic entities. 



We have seen that the hj-aline cytoplasm 

 consists of an enormous number of molec- 

 ular and submicroscopic particles ; that they 

 are mostly protein and probably range in 

 size from about 50 A up to nearly 5000 A 

 where they come just within the visible 

 range. We have seen also from models how 

 the pej^tide chains of many amino acids may 



