The Nature of Thermodynamic Coupling in Transport Processes
In considering problems of transport in (biological systems, the definitive role of the numerous membranes as evidenced by electron microscopy (Robertson 1960, Pa1ade 1964) is yet to be elucidated. These membranes appear to delineatemot only the limits of the individual cells, but (indeed many of the subcellular Sitructures as well. In an extremely complex fashion, membranes are involved in forming the cytoplasmic structure per se and are a prominent feature of the internal structure of subcellular elements. Attention in the past has been directed largely to those transport processes which are envisaged to occur transmembranally, that is across those barriers whose thickness is about 100 Å. However, attention should also be directed to the possibility that such membranes may play a major role in defining and directing cytoplasmic fluid flow processes within the cell. Cytoplasmic circulation, known to occur in living cells, may well represent more than the random mixing and stirring of the cytoplasmic contents. It may be considerably more fundamental in relation to the detailed functioning of the cell. For instance, it is difficult to imagine how m-RNA, synthesized in the nucleus, could in its random-coiled state and moving by simple random diffusion, avoid becoming hopelessly entangled in the nuclear and cytoplasmic substructure.
KeywordsReciprocal Relation Adenosine Triphosphatase Active Transport System Toad Bladder Cytoplasmic Flow
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