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Fig. 1 | Journal of Biological Engineering

Fig. 1

From: The engineering principles of combining a transcriptional incoherent feedforward loop with negative feedback

Fig. 1

Incoherent feed-forward loops in biology and engineering. a In biology, a Type 1 incoherent feedforward loop (I1-FFL) is characterized as an input, X, which activates both an intermediate (Y) and the ultimate output (Z), while Y represses or inhibits Z. b Illustration an I1-FFL gene regulatory motif. Input X binds to the regulatory regions of both Y and Z with affinity K1, and Y binds to the regulatory region of Z with affinity K2. X and Y may bind the regulatory region of Z cooperatively with a multiplicative factor C. c Illustration of feedforward control in chemical engineering. The goal of process control is to minimize the response to a disturbance. Well-tuned feedforward control will result in only minimal change to the output upon a disturbance. d Illustration of the dynamics of an I1-FFL (modeled as described in B) in biology. Here, the goal is not to be completely insensitive to the input, X, but is often to have a sharp response (P large), followed by adaptation (f small)

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