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Related Concept Videos

Circadian Rhythms and Gene Regulation02:19

Circadian Rhythms and Gene Regulation

The biological clock is involved in many aspects of regulating complex physiology in all animals. It was in 1935 when German zoologists, Hans Kalmus and Erwin Bünning, discovered the existence of circadian rhythm in Drosophila melanogaster. However, the internal molecular mechanisms behind the circadian clock remained a mystery until 1984, when Jeffrey C. Hall, Michael Rosbash, and Michael W. Young discovered the expression of the Per gene oscillating over a 24-hour cycle. In subsequent years,...
Circadian Rhythms and Gene Regulation02:19

Circadian Rhythms and Gene Regulation

The biological clock is involved in many aspects of regulating complex physiology in all animals. It was in 1935 when German zoologists, Hans Kalmus and Erwin Bünning, discovered the existence of circadian rhythm in Drosophila melanogaster. However, the internal molecular mechanisms behind the circadian clock remained a mystery until 1984, when Jeffrey C. Hall, Michael Rosbash, and Michael W. Young discovered the expression of the Per gene oscillating over a 24-hour cycle. In subsequent years,...
Biological Clocks and Seasonal Responses02:45

Biological Clocks and Seasonal Responses

The circadian—or biological—clock is an intrinsic, timekeeping, molecular mechanism that allows plants to coordinate physiological activities over 24-hour cycles called circadian rhythms. Photoperiodism is a collective term for the biological responses of plants to variations in the relative lengths of dark and light periods. The period of light-exposure is called the photoperiod.
Feedback Loops01:01

Feedback Loops

In most cases, excessive hormone production is prevented by negative feedback—a loop that starts with a stimulus inducing the release of a particular substance, like a hormone, to maintain a certain level before triggering a signal that results in a decrease in further release of the hormone.
Cell Signaling Feedback Loops01:07

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...
Positive and Negative Feedback Loops01:18

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:

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Updated: May 24, 2026

Parallel Measurement of Circadian Clock Gene Expression and Hormone Secretion in Human Primary Cell Cultures
06:53

Parallel Measurement of Circadian Clock Gene Expression and Hormone Secretion in Human Primary Cell Cultures

Published on: November 11, 2016

(Re)inventing the circadian feedback loop.

Steven A Brown1, Elzbieta Kowalska, Robert Dallmann

  • 1Institute of Pharmacology and Toxicology, University of Zürich, Zurich, Switzerland. steven.brown@pharma.uzh.ch

Developmental Cell
|March 17, 2012
PubMed
Summary
This summary is machine-generated.

Circadian clocks may be simpler than previously thought. New research suggests complex timekeeping evolved from basic feedback loops, challenging the long-held transcription-translation model.

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In Vivo Monitoring of Circadian Clock Gene Expression in the Mouse Suprachiasmatic Nucleus Using Fluorescence Reporters
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In Vivo Monitoring of Circadian Clock Gene Expression in the Mouse Suprachiasmatic Nucleus Using Fluorescence Reporters

Published on: July 4, 2018

Related Experiment Videos

Last Updated: May 24, 2026

Parallel Measurement of Circadian Clock Gene Expression and Hormone Secretion in Human Primary Cell Cultures
06:53

Parallel Measurement of Circadian Clock Gene Expression and Hormone Secretion in Human Primary Cell Cultures

Published on: November 11, 2016

In Vivo Monitoring of Circadian Clock Gene Expression in the Mouse Suprachiasmatic Nucleus Using Fluorescence Reporters
07:44

In Vivo Monitoring of Circadian Clock Gene Expression in the Mouse Suprachiasmatic Nucleus Using Fluorescence Reporters

Published on: July 4, 2018

Area of Science:

  • Chronobiology
  • Molecular Biology
  • Genetics

Background:

  • For two decades, circadian clocks were primarily understood through transcription-translation feedback loops.
  • Recent discoveries highlight posttranslational circadian oscillators across various species, necessitating a paradigm shift.

Purpose of the Study:

  • To review self-sustained clock mechanisms.
  • To propose simpler minimum requirements for diurnal timekeeping compared to free-running circadian oscillators.
  • To explore the evolutionary origins of complex circadian timekeeping.

Main Methods:

  • Literature review of existing research on circadian clock mechanisms.
  • Analysis of feedback loop structures in canonical and novel circadian oscillators.
  • Theoretical modeling of timekeeping requirements.

Main Results:

  • Canonical circadian clocks involve intricate interlocked feedback loops with numerous proteins.
  • Minimum requirements for basic diurnal timekeeping may be less complex than free-running oscillators.
  • Complex circadian timekeeping might have evolved from simpler, independent feedback loops.

Conclusions:

  • The traditional view of circadian clocks solely based on transcription-translation needs reevaluation.
  • Posttranslational oscillators represent a significant addition to our understanding of circadian biology.
  • Evolutionary pathways suggest complex circadian systems may arise from simpler, interconnected timekeeping modules.