The interactions of the proteins produced within a cell govern the fate of that cell. These protein interactions occur at two main levels: the extranuclear level and the intranuclear level. This presentation will focus on a particular Signal Transduction Pathway (STD) to illustrate the extranuclear level protein-protein interactions. As an example, the model will consider the events that begin with the binding of a ligand to a specific receptor (FGF) followed by the activation of a specific STD pathway that is downstream of the receptor. The events of this STD pathway will initiate the production/activation of some intranuclear proteins that in turn will release a cell from cell arrest, driving the cell through the cell cycle and resulting in cell proliferation. A detailed mathematical model that begins with FGF receptor activation, followed by MAP kinase pathway activation will be presented. The numerical simulations of the model and some qualitative and semi-quantitative experimental evidence will be discussed.