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Related Concept Videos

Photosystem I01:27

Photosystem I

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Although structurally similar to photosystem II (PSII), photosystem I (PSI) is has a different electron supplier and electron acceptor.
Both these photosystems work in concert. An excited electron from PSII is relayed to PSI via an electron transport chain in the thylakoid membrane of the chloroplast, which is comprised of the carrier molecule plastoquinone, the dual-protein cytochrome complex, and plastocyanin. As electrons move between PSII and PSI, they lose energy and must be re-energized...
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Photosystem II01:22

Photosystem II

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The multi-protein complex photosystem II (PS II) harvests photons and transfers their energy through its bound pigments to its reaction center, and ultimately to photosystem I (PSI) through the electron transport chain. The pigments responsible for caputirng the light energy in photosystems include chlorophyll a, chlorophyll b, and carotenoids.
The pigment molecules are arranged across  two photosystem domains — the antenna complex and the reaction center. The main aim of the pigment...
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The Z-Scheme of Electron Transport in Photosynthesis01:34

The Z-Scheme of Electron Transport in Photosynthesis

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The light reactions of photosynthesis assume a linear flow of electrons from water to NADP+. During this process, light energy drives the splitting of water molecules to produce oxygen. However, oxidation of water molecules is a thermodynamically unfavorable reaction and requires a strong oxidizing agent. This is accomplished by the first product of light reactions: oxidized P680 (or P680+), the most powerful oxidizing agent known in biology. The oxidized P680 that acquires an electron from the...
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Photosystems01:32

Photosystems

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Photosystems are multiprotein complexes that form the functional units of photosynthesis in plants, algae, and cyanobacteria. They are found embedded in the membrane of tiny sac-like structures called thylakoids placed inside the chloroplast.
Functioning of Photosystems
Photosystems contain many pigment molecules, such as chlorophylls and carotenoids, arranged in a particular organization across two domains — the antenna complex and the reaction center. The main aim of the pigment...
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The Photochemical Reaction Center01:29

The Photochemical Reaction Center

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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...
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Electron Transport Chain: Complex I and II01:46

Electron Transport Chain: Complex I and II

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The mitochondrial electron transport chain (ETC) is the main energy generation system in the eukaryotic cells. However, mitochondria also produce cytotoxic reactive oxygen species (ROS) due to the large electron flow during oxidative phosphorylation. While Complex I is one of the primary sources of superoxide radicals, ROS production by Complex II is uncommon and may only be observed in cancer cells with mutated complexes.
ROS generation is regulated and maintained at moderate levels necessary...
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Related Experiment Video

Updated: Mar 24, 2026

Purification of Active Photosystem I-Light Harvesting Complex I from Plant Tissues
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Purification of Active Photosystem I-Light Harvesting Complex I from Plant Tissues

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Modeling electron transfer in photosystem I.

Hiroki Makita1, Gary Hastings1

  • 1Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303, USA.

Biochimica Et Biophysica Acta
|March 21, 2016
PubMed
Summary

Electron transfer in Photosystem I was studied using spectroscopy and Marcus theory. The study determined specific in situ redox potentials for quinones, crucial for understanding electron flow in photosynthesis.

Keywords:
A(1)Electron transferEnergeticsKinetic modelingPhotosystem IPhylloquinone

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Studying the Supramolecular Organization of Photosynthetic Membranes within Freeze-fractured Leaf Tissues by Cryo-scanning Electron Microscopy
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Area of Science:

  • Biophysics
  • Photosynthesis research
  • Electron transfer mechanisms

Background:

  • Photosystem I (PSI) is crucial for photosynthesis, facilitating light-driven electron transport.
  • Understanding electron transfer kinetics in PSI is key to deciphering photosynthetic efficiency.

Purpose of the Study:

  • To investigate electron transfer dynamics in PSI using time-resolved absorption spectroscopy.
  • To determine the in situ midpoint potentials of various quinones within the A1 binding site of PSI.
  • To elucidate the relationship between quinone structure and electron transfer efficiency.

Main Methods:

  • Time-resolved absorption spectroscopy (nanosecond to millisecond) at 298 K and 77 K.
  • Incorporation of eight different quinones into the A1 binding site of PSI particles from Synechocystis sp. PCC 6803.
  • Kinetic modeling within Marcus electron transfer theory.

Main Results:

  • A detailed kinetic model successfully described experimental data, requiring quinone in situ midpoint potentials within a narrow range.
  • For phylloquinone in PSI, in situ midpoint potentials were -635 mV (A branch) and -690 mV (B branch).
  • Forward electron transfer from A(1)(-) to F(X) is slightly endergonic/exergonic on the A/B branches, with a reorganization energy of ~0.7 eV.

Conclusions:

  • The study established in situ redox potentials for eight incorporated quinones, correlating linearly with in vitro potentials.
  • The findings provide critical insights into the energetic requirements for efficient electron transfer in Photosystem I.
  • The precise determination of midpoint potentials refines our understanding of electron channeling in photosynthetic complexes.