 
Summary: Discrete dynamic modeling of biological
systemsy
ˇ The functional form of regulatory relationships and kinetic parameters
are often unknown
ˇ Increasing evidence for
ˇ robustness to changes in kinetic parameters.
ˇ bistability (two steady states)y ( y )
Hypothesis: the kinetic details of individual interactions are less
important than the organization of the regulatory networkimportant than the organization of the regulatory network
Discrete dynamic models assume that nodes can be characterized by
only a few (minimum two) discrete states.
Discrete models can handle larger networks than continuous models.g
Boolean modeling of biological systems
Main assumption: components have two main states :
Expressed or not expressed, active or inactive, open or closed (ionp p , , p (
channel), high or low level. Denote these states by ON (1) or OFF (0)
The changes in state are given by discrete (logical) rulesThe changes in state are given by discrete (logical) rules.
The future state of a regulated node (the output) depends on the
current state of its regulators (inputs), which may or may not include
its own current state.
