The cell division cycle is the sequence of events whereby a living cell replicates its components and divides them between two daughter cells, so that each daughter has the information and machinery necessary to repeat the process. Because cell proliferation underlies the growth, development and reproduction of all biological organisms, its molecular control mechanisms have come under intense scrutiny. We now know most of the central components controlling DNA replication and division of yeast cells, and there are good reasons to believe that mammalian cell cycle controls are elaborations on the same basic themes. This knowledge should be of great value in the health sciences and the biotechnology industry, but its application is limited by the very extent of the information. Bits and pieces of the puzzle are scattered throughout thousands of publications, the relative importance of different bits is often unclear, and how the pieces fit together is a combinatorial nightmare. Furthermore, the control system is not a static jigsaw puzzle but a dynamic machine whose function unfolds in space and time. To overcome these problems, we have been building ever more comprehensive and accurate models of the machinery controlling DNA synthesis, mitosis and division in budding and fission yeast cells. The models are analyzed by modern tools of dynamical systems like numerical simulations, phaseplane technique and bifurcations analysis. This kind of analysis shows that classical cell cycle phases (G1, S, G2 and M) represent stable steady states and the characteristic cell cycle transitions that happen at G1/S, G2/M boundary and at the meta/anaphase transition are characteristic bifurcations between these steady states.
