Limits...
Biological systems from an engineer's point of view.

Reeves GT, Fraser SE - PLoS Biol. (2009)

View Article: PubMed Central - PubMed

Affiliation: Biological Imaging Center, Beckman Institute, Division of Biology, California Institute of Technology, Pasadena, California, USA.

AUTOMATICALLY GENERATED EXCERPT
Please rate it.

Mathematical modeling of the processes that pattern embryonic development (often called biological pattern formation) has a long and rich history... If the decay constant, μ, is increased, the solid line shown in Figure 1C shifts to the dotted line... Correspondingly, the steady state value of c decreases to the open circle... Engineered systems were designed with a particular purpose in mind, so it would be helpful to ask, “What is/are the purpose(s) of this biological system?” Lander has called these purposes “performance objectives,” and determining what they are for a particular biological system is especially important in light of design trade-offs, and furthermore will provide clues to a system's molecular behavior... To demonstrate, let us return our simple example in Figure 1... We had originally assumed the removal rate of the enzyme was first-order, partially due to a dilution effect: enzyme concentration decreases as the cell grows in volume... In this issue of PLoS Biology, Lander and colleagues illustrate the utility of taking an engineer's perspective in the context of the olfactory neuron cell lineage in the mammalian olfactory epithelium (OE)... Thus, as the tissue grows, inhibitor concentration increases, slowly stalling and eventually ceasing cell division... Any loss of tissue results in a decrease in inhibitor concentration, leading to a proliferative phase for the stem and precursor cells to replace the lost tissue... In further analysis, Lander et al. focus on several experimentally observed performance objectives—including rapid regeneration after injury, low progenitor load (stem plus precursor cells make up less than 10% of the OE), and robustness of the steady state—and ask whether feedback loops could be designed to simultaneously meet these objectives... On the other hand, some readers would be skeptical of results that so heavily focus on the mathematics... This is not an unfounded skepticism, as evinced by numerous mathematical models in biology that have failed to accurately describe experimental systems... The authors begin with very general arguments from physics and mathematics, which correctly describe the overall behavior of a cell lineage without feedback, and have no need to model further detail... Indeed, a more detailed model would necessarily behave in a qualitatively similar fashion, but would muddy the water on the conclusions... Their model is sufficient to show that feedback is vital to the stability and robustness of any such lineage.

Show MeSH

Related in: MedlinePlus

Examples of Control Loops(A) Schematic of a simple control loop. The process output is monitored by a sensor, and the value of this output signal is passed to a device called a controller. The controller calculates the difference between the output signal and the set point (the desired value of the output), and responds accordingly, often by physically manipulating an input parameter, such as a control valve.(B) Schematic of cruise control. The car is the process, and the car's speed is the output. A speedometer sensor within the car tells the cruise control the car's speed. The actuator on the cruise control then responds by opening or closing the throttle, allowing air intake into the engine.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2628404&req=5

pbio-1000021-g002: Examples of Control Loops(A) Schematic of a simple control loop. The process output is monitored by a sensor, and the value of this output signal is passed to a device called a controller. The controller calculates the difference between the output signal and the set point (the desired value of the output), and responds accordingly, often by physically manipulating an input parameter, such as a control valve.(B) Schematic of cruise control. The car is the process, and the car's speed is the output. A speedometer sensor within the car tells the cruise control the car's speed. The actuator on the cruise control then responds by opening or closing the throttle, allowing air intake into the engine.

Mentions: The engineering and applied mathematics subfield of “control theory” refers to the use of feedback loops to ensure that system outputs, such as product purity, are maintained at set values (see general control loop in Figure 2A). Cruise control (now standard on most cars) is an everyday example of a feedback control system. When at the desired speed, the driver implements the set point by pushing the “set” button. Thereafter, the controller calculates the difference between the current speed and the set point, and opens or closes the throttle accordingly (Figure 2B). In reality, the controller uses not only the current difference (proportional control), but also the time history of the difference (integral control) and how fast that difference is changing (derivative control) to decide how strongly to respond. As each of the control strategies has inherent advantages and disadvantages, rarely do engineers implement only one control strategy at a time; most often controllers are of the PI (combining proportional and integral) or PID (combining all three) type.


Biological systems from an engineer's point of view.

Reeves GT, Fraser SE - PLoS Biol. (2009)

Examples of Control Loops(A) Schematic of a simple control loop. The process output is monitored by a sensor, and the value of this output signal is passed to a device called a controller. The controller calculates the difference between the output signal and the set point (the desired value of the output), and responds accordingly, often by physically manipulating an input parameter, such as a control valve.(B) Schematic of cruise control. The car is the process, and the car's speed is the output. A speedometer sensor within the car tells the cruise control the car's speed. The actuator on the cruise control then responds by opening or closing the throttle, allowing air intake into the engine.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2628404&req=5

pbio-1000021-g002: Examples of Control Loops(A) Schematic of a simple control loop. The process output is monitored by a sensor, and the value of this output signal is passed to a device called a controller. The controller calculates the difference between the output signal and the set point (the desired value of the output), and responds accordingly, often by physically manipulating an input parameter, such as a control valve.(B) Schematic of cruise control. The car is the process, and the car's speed is the output. A speedometer sensor within the car tells the cruise control the car's speed. The actuator on the cruise control then responds by opening or closing the throttle, allowing air intake into the engine.
Mentions: The engineering and applied mathematics subfield of “control theory” refers to the use of feedback loops to ensure that system outputs, such as product purity, are maintained at set values (see general control loop in Figure 2A). Cruise control (now standard on most cars) is an everyday example of a feedback control system. When at the desired speed, the driver implements the set point by pushing the “set” button. Thereafter, the controller calculates the difference between the current speed and the set point, and opens or closes the throttle accordingly (Figure 2B). In reality, the controller uses not only the current difference (proportional control), but also the time history of the difference (integral control) and how fast that difference is changing (derivative control) to decide how strongly to respond. As each of the control strategies has inherent advantages and disadvantages, rarely do engineers implement only one control strategy at a time; most often controllers are of the PI (combining proportional and integral) or PID (combining all three) type.

View Article: PubMed Central - PubMed

Affiliation: Biological Imaging Center, Beckman Institute, Division of Biology, California Institute of Technology, Pasadena, California, USA.

AUTOMATICALLY GENERATED EXCERPT
Please rate it.

Mathematical modeling of the processes that pattern embryonic development (often called biological pattern formation) has a long and rich history... If the decay constant, μ, is increased, the solid line shown in Figure 1C shifts to the dotted line... Correspondingly, the steady state value of c decreases to the open circle... Engineered systems were designed with a particular purpose in mind, so it would be helpful to ask, “What is/are the purpose(s) of this biological system?” Lander has called these purposes “performance objectives,” and determining what they are for a particular biological system is especially important in light of design trade-offs, and furthermore will provide clues to a system's molecular behavior... To demonstrate, let us return our simple example in Figure 1... We had originally assumed the removal rate of the enzyme was first-order, partially due to a dilution effect: enzyme concentration decreases as the cell grows in volume... In this issue of PLoS Biology, Lander and colleagues illustrate the utility of taking an engineer's perspective in the context of the olfactory neuron cell lineage in the mammalian olfactory epithelium (OE)... Thus, as the tissue grows, inhibitor concentration increases, slowly stalling and eventually ceasing cell division... Any loss of tissue results in a decrease in inhibitor concentration, leading to a proliferative phase for the stem and precursor cells to replace the lost tissue... In further analysis, Lander et al. focus on several experimentally observed performance objectives—including rapid regeneration after injury, low progenitor load (stem plus precursor cells make up less than 10% of the OE), and robustness of the steady state—and ask whether feedback loops could be designed to simultaneously meet these objectives... On the other hand, some readers would be skeptical of results that so heavily focus on the mathematics... This is not an unfounded skepticism, as evinced by numerous mathematical models in biology that have failed to accurately describe experimental systems... The authors begin with very general arguments from physics and mathematics, which correctly describe the overall behavior of a cell lineage without feedback, and have no need to model further detail... Indeed, a more detailed model would necessarily behave in a qualitatively similar fashion, but would muddy the water on the conclusions... Their model is sufficient to show that feedback is vital to the stability and robustness of any such lineage.

Show MeSH
Related in: MedlinePlus