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Related Concept Videos

Protein Transport to the Inner Chloroplast Membrane01:18

Protein Transport to the Inner Chloroplast Membrane

Proteins targeted to the inner chloroplast membrane, or plastid proteins, are transported by two general pathways: the stop-transfer and the re-insertion or post-import pathways. Most plastid proteins carry N-terminal transit sequences and internal import sequences targeting it to the specific chloroplast subcompartment. Proteins targeted by the stop-transfer pathway have internal hydrophobic sequences that inhibit their translocation into the stroma. As a result, these precursors are arrested...
The Anatomy of Chloroplasts01:08

The Anatomy of Chloroplasts

Green algae and plants, including green stems and unripe fruit, harbor specialized organelles called chloroplasts to carry out photosynthesis. They coordinate both stages of photosynthesis — the light-dependent reactions and the light-independent reactions. The light-dependent reactions use sunlight to release oxygen and produce chemical energy in the form of ATP and NADPH, and the light-independent reactions capture CO2 and use ATP and NADPH to produce sugar.
Structure of Chloroplasts
A...
Protein Transport to the Outer Chloroplast Membrane01:11

Protein Transport to the Outer Chloroplast Membrane

Chloroplast outer membrane proteins encoded by the nucleus are synthesized in the cytosol. Soon after synthesis, they bind cytosolic factors such as 14-3-3 protein and the Hsp70 chaperones that keep these precursors in an unfolded state until their translocation.
Two models describe the mechanism of precursor recognition and entry across the outer membrane through the TOC complex. Model 1 suggests the newly synthesized precursor binds to the TOC receptor 159 and forms a complex.
Protein Transport to the Stroma01:24

Protein Transport to the Stroma

Chloroplasts are triple membrane structures with an outer membrane, an inner membrane, and a thylakoid membrane, each containing distinct metabolite transporters, membrane translocons, and enzymes. Appropriate sorting and translocating these proteins to their correct membrane systems is essential for chloroplast function.
Protein complexes called the translocon of the outer chloroplast membrane or TOC complex, and the translocon of the inner chloroplast membrane or TIC complex mediate the...
Comparing Mitochondrial, Chloroplast, and Prokaryotic Genomes02:16

Comparing Mitochondrial, Chloroplast, and Prokaryotic Genomes

The present-day mitochondrial and chloroplast genomes have retained some of the characteristics of their ancestral prokaryotes and also have acquired new attributes during their evolution within eukaryotic cells. Like prokaryotic genomes, mitochondrial and chloroplast genomes neither bind with histone-like proteins nor show complex packaging into chromosome-like structures, as observed in eukaryotes. Unlike mitotic cell divisions observed in eukaryotic cells, mitochondria and chloroplasts...
Anatomy of Chloroplasts01:07

Anatomy of Chloroplasts

Green algae and plants, including green stems and unripe fruit, harbor chloroplasts—the vital organelles where photosynthesis takes place. In plants, the highest density of chloroplasts is found in the mesophyll cells of leaves.

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Related Experiment Video

Updated: May 30, 2026

Studying Protein Import into Chloroplasts Using Protoplasts
06:29

Studying Protein Import into Chloroplasts Using Protoplasts

Published on: December 10, 2018

Chloroplast Omp85 proteins change orientation during evolution.

Maik S Sommer1, Bertram Daum, Lucia E Gross

  • 1Cluster of Excellence Frankfurt, Goethe University, D-60438 Frankfurt, Germany.

Proceedings of the National Academy of Sciences of the United States of America
|August 10, 2011
PubMed
Summary
This summary is machine-generated.

Outer membrane proteins (OMPs) assembly is crucial. This study reveals the POTRA domains of chloroplast Omp85 proteins face the cytoplasm, challenging existing models of OMP biogenesis and TOC complex function.

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Using Changes in Leaf Transmission to Investigate Chloroplast Movement in Arabidopsis thaliana
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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

Last Updated: May 30, 2026

Studying Protein Import into Chloroplasts Using Protoplasts
06:29

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Published on: December 10, 2018

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Separation of Spinach Thylakoid Protein Complexes by Native Green Gel Electrophoresis and Band Characterization using Time-Correlated Single Photon Counting
08:40

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

Published on: February 14, 2019

Area of Science:

  • Molecular Biology
  • Biochemistry
  • Cell Biology

Background:

  • Outer membrane proteins (OMPs) are essential components of gram-negative bacteria, mitochondria, and chloroplasts, often forming β-barrel structures.
  • The Omp85 protein family catalyzes the insertion and assembly of OMPs, featuring conserved N-terminal POTRA domains and C-terminal β-barrel domains.
  • In plant chloroplasts, Toc75-III and Toc75-V are essential Omp85 homologs, with Toc75-V retaining ancestral function and Toc75-III forming the TOC translocon pore.

Purpose of the Study:

  • To investigate the topology of the POTRA domains of Toc75-III and Toc75-V within the chloroplast outer membrane.
  • To challenge and re-evaluate current models of outer membrane protein biogenesis and the function of the TOC complex.

Main Methods:

  • Utilized self-assembly GFP-based in vivo experiments to study protein localization.
  • Employed in situ topology studies using electron cryotomography for high-resolution structural analysis.

Main Results:

  • Demonstrated that the POTRA domains of both Toc75-III and Toc75-V are exposed to the cytoplasm.
  • This finding contradicts the widely assumed topology of Omp85 proteins with POTRA domains in the periplasm or intermembrane space.

Conclusions:

  • The cytoplasmic exposure of POTRA domains necessitates a reevaluation of established models for OMP biogenesis.
  • Current understanding of the TOC complex's function in preprotein import requires revision based on this unexpected topology.