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Related Concept Videos

Photosystem II01:22

Photosystem II

59.9K
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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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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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 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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The Photochemical Reaction Center01:29

The Photochemical Reaction Center

4.4K
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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Oxygenic Photosynthesis01:26

Oxygenic Photosynthesis

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Oxygenic photosynthesis is a fundamental process in which light energy is harnessed to drive the oxidation of water, leading to the production of molecular oxygen (O₂), adenosine triphosphate (ATP), and nicotinamide adenine dinucleotide phosphate (NADPH). This process is essential for sustaining aerobic life on Earth and is primarily carried out by cyanobacteria, algae, and plants. The core of oxygenic photosynthesis lies in the thylakoid membranes, where chlorophyll pigments facilitate...
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Related Experiment Video

Updated: May 4, 2026

A New Approach for the Comparative Analysis of Multiprotein Complexes Based on 15N Metabolic Labeling and Quantitative Mass Spectrometry
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A New Approach for the Comparative Analysis of Multiprotein Complexes Based on 15N Metabolic Labeling and Quantitative Mass Spectrometry

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Evidence for two types of electron transfer processes through Photosystem II.

Z Drechsler1, J Neumann

  • 1Department of Botany, The George S. Wise Faculty of Life Sciences, Tel Aviv University, 69978, Tel Aviv, Israel.

Photosynthesis Research
|January 16, 2014
PubMed
Summary

This study reveals two distinct electron transport chains in chloroplasts, differing in their sensitivity to 3-(3

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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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Separation of Spinach Thylakoid Protein Complexes by Native Green Gel Electrophoresis and Band Characterization using Time-Correlated Single Photon Counting
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Separation of Spinach Thylakoid Protein Complexes by Native Green Gel Electrophoresis and Band Characterization using Time-Correlated Single Photon Counting

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Related Experiment Videos

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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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Area of Science:

  • Photosynthesis research
  • Plant biochemistry
  • Electron transport mechanisms

Background:

  • 3-(3',4'-dichlorophenyl)-1,1-dimethyl urea (DCMU) inhibits electron flow from H2O to methylviologen.
  • This inhibition exhibits biphasic kinetics with distinct high and low sensitivity phases.
  • These phases differ in pH dependence and light saturation requirements.

Purpose of the Study:

  • To investigate the differential effects of chemical treatments on the two phases of photosynthetic electron flow.
  • To elucidate the structural and functional basis for the differential sensitivity to DCMU.
  • To identify the role of specific components like iron and redox potential in electron transport regulation.

Main Methods:

  • Utilized isolated chloroplasts and subjected them to various treatments: ferricyanide preincubation, Tris-treatment, and trypsin digestion.
  • Measured electron flow inhibition by DCMU under varying pH and redox potential conditions.
  • Analyzed DCMU's inhibitory mechanism as a competitive inhibitor with respect to [H(+)] in trypsinized chloroplasts.

Main Results:

  • Ferricyanide preincubation inhibited the high sensitivity phase, while Tris-treatment predominantly affected the low sensitivity phase.
  • Trypsin digestion, blocking electron flow between QA and QB, revealed DCMU sensitivity dependent on pH and redox potential.
  • Under specific conditions (negative redox potential during trypsin treatment), DCMU only inhibited the high sensitivity phase.

Conclusions:

  • The results strongly suggest the existence of two distinct types of electron transport chains.
  • One chain, sensitive to DCMU, likely involves a QA-Fe complex whose redox state influences electron flow.
  • The second, less sensitive chain, may lack iron or have oxidized, inaccessible iron, leading to DCMU insensitivity.