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Related Concept Videos

Photosystems01:32

Photosystems

5.8K
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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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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Structure of Porins01:21

Structure of Porins

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Mitochondria, chloroplasts, and gram-negative bacteria have transmembrane, beta-barrel proteins called porins to mediate the free diffusion of ions and metabolites across the membrane. Mitochondrial porin precursors contain conserved amino acid sequences called beta signals at their C-terminal. Beta signals have a  motif of PoXGXXHyXHy (Po-Polar, X-Any amino acid, G-Glycine, Hy-LargeHydrophobic), which are crucial for precursor recognition to initiate precursor assembly. Beta-barrel...
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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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Bacterial Phylum Cyanobacteria01:30

Bacterial Phylum Cyanobacteria

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Cyanobacteria are a diverse group of oxygenic, phototrophic bacteria that played a pivotal role in converting Earth’s atmosphere from anoxic to oxygen-rich billions of years ago. They exhibit remarkable morphological diversity, ranging from unicellular forms to filamentous types, with cell sizes varying between 0.5 μm and 100 μm. Cyanobacteria are classified into five groups: Chroococcales (unicellular, dividing by binary fission), Pleurocapsales (unicellular, dividing by...
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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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Related Experiment Video

Updated: Nov 6, 2025

Isolation and Characterization of Intact Phycobilisome in Cyanobacteria
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Isolation and Characterization of Intact Phycobilisome in Cyanobacteria

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Structure of Phycobilisomes.

Sen-Fang Sui1

  • 1State Key Laboratory of Membrane Biology, Beijing Advanced Innovation Center for Structural Biology and Frontier Research Center for Biological Structure, School of Life Sciences, Tsinghua University, Beijing 100084, China;

Annual Review of Biophysics
|May 6, 2021
PubMed
Summary

Phycobilisomes (PBSs) are large complexes that harvest light energy for photosynthesis in algae and cyanobacteria. This review details their structure and the crucial role of linker proteins in energy transfer.

Keywords:
cryo-EMenergy transfer in photosynthesislinker proteinphycobilisomered algaeπ–π interactions

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Area of Science:

  • Photosynthesis research
  • Structural biology
  • Algal and cyanobacterial biochemistry

Background:

  • Phycobilisomes (PBSs) are massive light-harvesting complexes found in cyanobacteria and red algae.
  • They are located on the stromal side of the thylakoid membrane and function as antennae for photosystems I and II.
  • PBSs consist of phycobiliproteins and linker proteins, essential for efficient light energy capture and transfer.

Purpose of the Study:

  • To review the detailed structures of phycobilisomes in red algae species like *Griffithsia pacifica* and *Porphyridium purpureum*.
  • To elucidate the specific functions of linker proteins in the assembly of phycobilisomes.
  • To understand how linker proteins fine-tune the energy state of chromophores within PBSs for optimal light harvesting.

Main Methods:

  • Structural analysis of phycobilisomes from *Griffithsia pacifica* and *Porphyridium purpureum*.
  • Biochemical investigation of phycobiliprotein and linker protein interactions.
  • Spectroscopic analysis to determine chromophore energy states and transfer efficiencies.

Main Results:

  • Detailed structural insights into the organization of phycobilisomes in the studied red algae.
  • Identification of specific roles for linker proteins in mediating phycobiliprotein assembly.
  • Demonstration of how linker proteins modulate chromophore energy levels for efficient light harvesting.

Conclusions:

  • The structure and function of phycobilisomes are critical for efficient photosynthesis in red algae.
  • Linker proteins play indispensable roles in both the assembly and the photophysical properties of phycobilisomes.
  • Understanding these molecular mechanisms provides fundamental insights into light energy conversion in photosynthetic organisms.