| Abstract: |
The G1 phase is the most variable part of the cell cycle. Transit through G1 is regulated by a chain of syntheses of specific substances (probably proteins), promoted by extracellular "growth factors". When the last substance of the chain reaches the threshold concentration, DNA synthesis can be initiated. We propose a model in the form of a chain of nonlinear ordinary differential equations. When all the constants representing extracellular growth factors are nonzero, the system proceeds towards a unique equilibrium. Moreover, in a special case it is demonstrated that the concentration of the last element of the chain is an increasing time function. When one or more of the "growth factor" constants are set equal to zero, part of the system becomes extinct while the remaining subsystem does not possess an equilibrium. Biological relevance of this model is discussed. © 1989. |
