Biochemical reactions, cell dimensions

Chemical and biochemical reactions can be viewed by diffraction methods provided the reactions are slow and the techniques for measuring them are rapid. For example, Lonsdale and coworkers studied the conversion of a photo-oxide of anthracene on exposure to Cu Ka or Mo Ka X rays at room temperature. A single mixed crystal of anthraquinone and anthrone is formed which still shows crystallinity. The crystal does not change in appearance, and the space group remains P2i/a, but the unit-cell dimensions change ... 

All these considerations are basic and equally applicable to the broad variety of biochemical reaction systems. We can use them to determine the optimal size of catalyst particles in a giant petroleum cracking process but they have interdisciplinary, i.e. universal applicability to any molecular process systems (2.) including the biochemical transformation processes at the dimensions of organs, cells, organelles, and smaller molecular units. 

Paul Weisz suggested in a lucid note published in 1973 that cells, and indeed even entire organisms, have evolved in a way that maintains unity effectiveness factor [24]. That is, the size of the catalytic assembly is increased in nature as the overall rate at which that assembly operates decreases, and the relationship between characteristic dimension and activity can be well approximated by the observable modulus criterion for reaction limitation. It is possible that Weisz s arguments may fail under process conditions, and internal gradients within a compartment or cell may be important. However, at present it appears that the most important transport limitations and activities in cells are those that operate across cellular membranes. Therefore, to understand and to manipulate key transport activities in cells, it is essential that biochemical engineers understand these membrane transport processes and the factors influencing their operation. A brief outline of some of the important systems and their implications in cell function and biotechnology follows. 

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