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Related Concept Videos

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.
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,...
Photoreceptors and Visual Pathways01:22

Photoreceptors and Visual Pathways

At the molecular level, visual signals trigger transformations in photopigment molecules, resulting in changes in the photoreceptor cell's membrane potential. The photon's energy level is denoted by its wavelength, with each specific wavelength of visible light associated with a distinct color. The spectral range of visible light, classified as electromagnetic radiation, spans from 380 to 720 nm. Electromagnetic radiation wavelengths exceeding 720 nm fall under the infrared category, whereas...
Channel Rhodopsins01:11

Channel Rhodopsins

Most organisms use photoreceptors to sense and respond to light. Examples of photoreceptors include bacteriorhodopsins and bacteriophytochromes in some bacteria, phytochromes in plants, and rhodopsins in the photoreceptor cells of the vertebral retina. The light-sensitive property of these receptors is because of the bound chromophores, such as bilin in the phytochromes and retinal in the rhodopsins.
Rhodopsins belong to the family of cell surface proteins called G-protein coupled receptors,...
Photoreceptors and Plant Responses to Light02:00

Photoreceptors and Plant Responses to Light

Light plays a significant role in regulating the growth and development of plants. In addition to providing energy for photosynthesis, light provides other important cues to regulate a range of developmental and physiological responses in plants.

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Related Experiment Video

Updated: Jul 5, 2026

In Vitro Bioluminescence Assay to Characterize Circadian Rhythm in Mammary Epithelial Cells
11:56

In Vitro Bioluminescence Assay to Characterize Circadian Rhythm in Mammary Epithelial Cells

Published on: September 28, 2017

Circadian photoreception in vertebrates.

S Doyle1, M Menaker

  • 1Department of Biology, University of Virginia, Charlottesville, Virginia 22936, USA.

Cold Spring Harbor Symposia on Quantitative Biology
|April 19, 2008
PubMed
Summary

Internal circadian clocks synchronize to daily rhythms using light. Mammals and nonmammalian vertebrates differ in photoreceptor location and type, suggesting specialized roles in entrainment and other light-mediated behaviors.

Area of Science:

  • Chronobiology
  • Neuroscience
  • Vision Science

Background:

  • Circadian clocks require entrainment to environmental rhythms, primarily light.
  • Vertebrates utilize specialized photoreceptors for synchronizing light signals.
  • Mammals and nonmammalian vertebrates exhibit distinct photoreceptor distributions and types.

Purpose of the Study:

  • To investigate the specialized roles of different photoreceptor classes in circadian entrainment.
  • To explore the differences in circadian photoreception between mammals and nonmammalian vertebrates.
  • To review early work on avian circadian systems and present new findings on mammalian photoreceptors.

Main Methods:

  • Review of early avian circadian research.
  • Analysis of new findings on mammalian retinal photoreceptors (rods, cones, intrinsically photosensitive retinal ganglion cells).

Related Experiment Videos

Last Updated: Jul 5, 2026

In Vitro Bioluminescence Assay to Characterize Circadian Rhythm in Mammary Epithelial Cells
11:56

In Vitro Bioluminescence Assay to Characterize Circadian Rhythm in Mammary Epithelial Cells

Published on: September 28, 2017

  • Comparison of photoreceptor systems across vertebrate groups.

    • Main Results:

    • Mammals concentrate circadian photoreceptors in the retina, including rods, cones, and melanopsin-containing retinal ganglion cells.
    • Nonmammalian vertebrates utilize photoreceptors in the retina, brain, and pineal gland.
    • Evidence suggests distinct roles for different photoreceptor types in entrainment and light-mediated behaviors.

    Conclusions:

    • The diversity of photoreceptor systems in vertebrates likely reflects specialized functions in circadian entrainment.
    • The mammalian nonvisual photoreceptive system regulates masking, pupillary response, and photoperiodism.
    • Further research is needed to fully elucidate the specific contributions of each photoreceptor class.