Scientific concept · BEGINNER LESSON
Control
Control is the ability to direct or command the behavior of a system, and it is measured by how strongly an input changes an output. In systems biology, control is quantified with control coefficients that show how much a parameter affects flux or concentration.
What control is
Control means the ability to direct or command the behavior of a system. In control theory, the main question is how much an input, such as a signal or parameter, changes an output, such as a temperature, flux, or concentration. To measure this, scientists use control coefficients, which compare the relative change in the output with the relative change in the input.
[1] Control and regulation of pathways via negative feedback - PMC [2] Figure 5: A Schematic For... [3] Control Theory and Systems Biology
How control works
Control theory studies systems with inputs, outputs, and feedback. A controller acts to reduce error between a desired state and the current state, while feedback helps keep the system near its target. In biology, elasticities describe how sensitively reaction rates respond to changes in reactants, products, or effectors, and these signal changes are transmitted through a network.
[1] Control and regulation of pathways via negative feedback - PMC [2] Figure 5: A Schematic For... [3] Control Theory and Systems Biology
Control versus regulation
Control and regulation are not the same. Control is the influence an outside agent or parameter has on a system, while regulation is the mechanism that produces the response. For example, in a temperature system, the chosen setting is control, and the sensors, feedback, and actuators are the regulation that makes the setting happen.
[1] Control and regulation of pathways via negative feedback - PMC [2] Figure 5: A Schematic For...
In cells and pathways
In metabolic pathways, control is often shared across several enzymes rather than owned by one step alone. A flux control coefficient describes how much an enzyme influences pathway flow, and a concentration control coefficient describes how much it changes the amount of a metabolite. Negative feedback can narrow the range of end product and flux, but weak signal transmission can still make regulation small.
[1] Control and regulation of pathways via negative feedback - PMC [3] Control Theory and Systems Biology
Limits of control analysis
Control theory is useful, but it has limits. Some models are computationally heavy, especially when they use ordinary differential equations, and results can depend on parameter estimates that are hard to measure well. A system also must be observable enough for its internal state to be inferred from measurements, and controllability is the ability to move it through its possible states.
[2] Figure 5: A Schematic For... [3] Control Theory and Systems Biology
SEE THE IDEA
Control in a feedback system
An external signal or parameter changes the system.
The measured result, such as flux, concentration, or temperature.
Sensors and actuators adjust the response to reduce error.
A number that summarizes how strongly the input changes the output.
Input changes the system; feedback shapes the response; the control coefficient measures the strength of that influence.
Control is the influence of an input on an output, while feedback is the mechanism that helps keep the output near its target.
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Sources and further reading
This general lesson was generated from public source material. It explains a concept; it does not interpret a private paper or provide medical advice.