Figure 2.

Multi-level rule-based model of yeast cell cycle regulation (after [10]). (a) Nested view of the model structure. The world node contains a population of cells, each of which has two attributes, volume and cell cycle state. Stacking of boxes representing each entity indicates a variable number of instances. Each cell contains a population of molecules that comprise the biochemical components of the cell cycle. (b) Upward causation - components of the molecular layer influence dynamics of the cell layer. The number of MPF molecules in the I state (for 'inactive') controls the passage from G1 to S. The formula beneath the arrow must be true in order for the rule to fire. (c) Downward causation - the state of the cell influences the rate of a biochemical transformation of contained molecules.

Faeder BMC Biology 2011 9:68   doi:10.1186/1741-7007-9-68
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