The normal and cancerous living cell

摘要

We do not have a definition of the living and cancerous states; we can give only their main characteristics at the different levels of organization: cell, organ, and organism. A simple model is proposed for a normal eukaryotic cell based on Prigogine's equation of chemical kinetics with diffusion. In this model, possibly only a few hundred key biochemical reactions should be selected together with their rate and diffusion constants. To solve these coupled nonlinear partial differential equation systems, it is proposed that the model cell be subdivided into compartments and that the problem be worked out always for one compartment (finite element method). This is possible, since the most important biochemical reactions and reaction cycles occur in different parts of the cell. The solutions (concentrations) obtained in one compartment can be used as input to the other compartments (together with the components entering from the environment). As an example, the problem of 10 reactions and 3 compartments has been solved by discretizing the space coordinates and choosing time steps. The solutions obtained by solving the 10 differential equations directly and by the compartmentalization agree very well. The main obstacles to further progress lie in the right choice of reactions and compartments, as well as in the correct estimation of the rate and diffusion constants, which were measured in only a few cases. If such a model cell can be obtained, the solutions should be investigated to determine (i) for their stability (homeostasis); (ii) whether changing the input concentrations to a larger degree one would obtain a new stationary state showing the characteristics of a precancerous state; and (iii) a method of extracting those input concentrations, or functions of them, which are the most important regulatory parameters. If successful, this would provide a scientific definition of the living state in the normal and cancerous states, respectively, at least at the cell level. Finally, outline is provided showing how the model might be extended to multicellular cases, as well as the main difficulties of such a process. (C) 2006 Wiley Periodicals, Inc.