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Related Concept Videos

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 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...
Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
The Photochemical Reaction Center01:29

The Photochemical Reaction Center

Reaction centers are pigment-protein complexes that initiate energy conversion from photons to chemical entities. Therefore, photochemical reaction center is a more appropriate term that describes these complexes. The Nobel laureates Robert Emerson and William Arnold provided the first experimental evidence of photochemical reaction centers by demonstrating the participation of nearly 2,500 chlorophyll molecules for the release of just one molecule of oxygen. Despite thousands of photosynthetic...
Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
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,...

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Related Experiment Video

Updated: Jun 23, 2026

Proton Transfer and Protein Conformation Dynamics in Photosensitive Proteins by Time-resolved Step-scan Fourier-transform Infrared Spectroscopy
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Published on: June 27, 2014

Evidence for a 13,14-cis cycle in bacteriorhodopsin.

P Tavan, K Schulten

    Biophysical Journal
    |May 12, 2009
    PubMed
    Summary
    This summary is machine-generated.

    This study compares experimental vibrational spectra of bacteriorhodopsin with theoretical calculations to validate its photo-cycle. Findings support the proposed sequence of intermediates, including specific isomer forms.

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    Published on: October 24, 2014

    Area of Science:

    • Biophysics
    • Spectroscopy
    • Computational Chemistry

    Background:

    • Bacteriorhodopsin's photo-cycle is crucial for understanding proton pumping.
    • Previous studies utilized resonance Raman and infrared absorption to observe spectral changes during the photo-cycle.
    • Discrepancies in spectral assignments necessitate further investigation.

    Purpose of the Study:

    • To evaluate the consistency of observed vibrational spectra with a proposed bacteriorhodopsin photo-cycle.
    • To investigate the influence of different charge environments on vibrational spectra using computational methods.

    Main Methods:

    • Utilized quantumchemical Modified Neglect of Diatomic Overlap (MNDO) calculations.
    • Calculated vibrational spectra for protonated retinal Schiff base isomers.
    • Analyzed the impact of charge environments on C-C single bond stretching vibrations.

    Main Results:

    • The study assessed the agreement between experimental data (Smith et al., Gerwert and Siebert) and theoretical predictions.
    • MNDO calculations provided insights into the vibrational characteristics of key photo-cycle intermediates.
    • The effect of charge environments on specific vibrational frequencies was elucidated.

    Conclusions:

    • The findings contribute to validating the proposed bacteriorhodopsin photo-cycle sequence (BR, I->K->L->M->N->O).
    • Computational vibrational spectra aid in assigning experimental observations.
    • Understanding charge environment effects refines spectral interpretation in biological systems.