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Related Concept Videos

Positive and Negative Feedback Loops

Positive and Negative Feedback Loops

Animal organs and organ systems constantly adjust to internal and external changes through a process called homeostasis ("steady state"). Examples of these changes include regulation of the level of glucose or calcium in the blood or internal responses to external temperatures. Homeostasis requires maintaining an internal dynamic equilibrium:

Cell Signaling Feedback Loops

Cell Signaling Feedback Loops

Positive and negative feedback loops are crucial for regulating biological signaling systems. These feedback loops are processes that connect output signals to their inputs.
Negative feedback loops
Most signaling systems have negative feedback loops that can perform different functions such as output limiter, and adaptation.
Output limiter
Upon receiving an input signal, the cellular response rapidly increases until a threshold is reached. Beyond this threshold, a negative feedback loop...

Effects of feedback

Effects of feedback

Feedback in control systems plays a critical role in shaping various operational parameters, extending beyond simple error reduction to influence stability, bandwidth, gain, impedance, and sensitivity. Understanding these effects requires examining a basic feedback system characterized by defined input, output, error, and feedback signals.
Feedback significantly modifies the gain of a control system. The gain of a system without feedback is altered by a factor of one plus GH, where G represents...

Feedback control systems

Feedback control systems

Feedback control systems are categorized in various ways based on their design, analysis, and signal types.
Linear feedback systems are theoretical models that simplify analysis and design. These systems operate under the principle that their output is directly proportional to their input within certain ranges. For instance, an amplifier in a control system behaves linearly as long as the input signal remains within a specific range. However, most physical systems exhibit inherent nonlinearity...

Root Loci for Positive-Feedback Systems

Root Loci for Positive-Feedback Systems

The Hartley oscillator is a positive feedback system that sustains oscillations by feeding the output back to the input in phase, thereby reinforcing the signal. Positive feedback systems can be viewed as negative feedback systems with inverted feedback signals. In these systems, the root locus encompasses all points on the s-plane where the angle of the system transfer function equals 360 degrees.
The construction rules for the root locus in positive feedback systems are similar to those in...

Negative and Positive Feedback

Negative and Positive Feedback

Animal organs and organ systems constantly adjust to internal and external changes through a process called homeostasis ("steady state"). Examples of these changes include regulation of the level of glucose or calcium in the blood or internal responses to external temperatures. Homeostasis requires maintaining an internal dynamic equilibrium:

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Related Experiment Video

Updated: Jul 18, 2026

Interactive and Visualized Online Experimentation System for Engineering Education and Research

Interactive and Visualized Online Experimentation System for Engineering Education and Research

Published on: November 24, 2021

Construction and engineering of positive feedback loops.

Daniel J Sayut, Yan Niu, Lianhong Sun

ACS Chemical Biology

|December 23, 2006

Summary

Researchers engineered highly sensitive genetic switches using artificial positive feedback loops (PFLs). These synthetic biology tools, based on LuxR activators, can be precisely controlled for gene expression applications.

Area of Science:

Synthetic biology
Genetic engineering
Molecular biology

Background:

Artificial positive feedback loops (PFLs) serve as genetic amplifiers for weak promoters.
PFLs are utilized in constructing eukaryotic gene switches.
The LuxR transcriptional activator and its cognate promoter, P_luxI, are key components in biological regulatory systems.

Purpose of the Study:

To construct and evolve artificial positive feedback loops (PFLs) for enhanced gene regulation.
To increase the sensitivity of PFLs for detecting low concentrations of inducers.
To explore the potential of these PFLs in building complex genetic networks.

Main Methods:

Construction of PFLs utilizing the LuxR transcriptional activator and P_luxI promoter.

Related Experiment Videos

Last Updated: Jul 18, 2026

Interactive and Visualized Online Experimentation System for Engineering Education and Research

Interactive and Visualized Online Experimentation System for Engineering Education and Research

Published on: November 24, 2021

Directed evolution of the LuxR activator to enhance PFL sensitivity.

Characterization of PFL activation thresholds using varying concentrations of 3-oxo-hexanoyl-homoserine lactone (OHHL).

Main Results:

Wild-type PFLs were fully activated by 10 nM OHHL.
Directed evolution yielded PFLs activated at 5 nM OHHL (approximately 3 molecules per cell).
The sensitivity and response of the PFLs were tunable by adjusting inducer concentrations.

Conclusions:

Highly sensitive and regulatable PFLs were successfully developed.
These advanced PFLs can be integrated into larger artificial genetic networks.
Potential applications include understanding biological design principles, industrial fermentation, and gene therapy.