Irreversible cell-cycle transitions are due to systems-level feedback.
Novak B., Tyson JJ., Gyorffy B., Csikasz-Nagy A.
The irreversibility of cell-cycle transitions is commonly thought to derive from the irreversible degradation of certain regulatory proteins. We argue that irreversible transitions in the cell cycle (or in any other molecular control system) cannot be attributed to a single molecule or reaction, but that they derive from feedback signals in reaction networks. This systems-level view of irreversibility is supported by many experimental observations.