Diffusion and Perfusion in the Living Cell: Implications for Metabolic Regulation and Organization
A tacit assumption throughout much of biology, based on the smallness of size of most metazoan cells, is that diffusion of molecules within the cytoplasm suffices for metabolic purposes. This long-standing premise is challenged. Because cells are rich in protein (20% or more on average), it follows that, irrespective of whether this macromolecular material exists mostly in true solution (which is most improbable) or out of solution in the form of an elaborate cytomatrix and cytoskeleton, the random movements of molecules (especially large and/or reactive ones) will be impeded. However, since molecules of all sizes can be distributed throughout the cytoplasm within a matter of a second or two, the presence of a system which facilitates dispersion is indicated.
KeywordsDelivery Rate Simple Diffusion Cytoplasmic Streaming Bulk Aqueous Phase Insoluble Phase
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