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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...
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 Thylakoids01:22

Protein Transport to the Thylakoids

Thylakoids are membrane-bound sac-like structures within the chloroplast that serve as sites for photosynthesis. Thylakoid lumen contains many electron transport proteins and is enclosed by a thylakoid membrane rich in the light-harvesting complex. Proteins targeted to the thylakoids are transported as precursors and are sorted by the general TOC/TIC import pathway. Once the precursor reaches the stroma, stromal processing peptidases remove their transit signal and expose thylakoid signal...
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...
Overview of Protein Sorting and Transport01:45

Overview of Protein Sorting and Transport

Eukaryotic cells have different membrane-bound organelles with distinct protein requirements. The process by which proteins are targeted to a specific organelle is called protein sorting.
Protein sorting can be of two types: signal-based sorting and vesicle-based trafficking. In signal-based sorting, specific amino acid sequences called sorting signals target proteins to the proper location inside the cell either via gated transport or by protein translocation.  In gated transport, folded...
Translocation of Proteins into the Mitochondria01:19

Translocation of Proteins into the Mitochondria

Mitochondrial precursors are translocated to the internal subcompartments via independent mechanisms involving distinct protein machineries called translocases.
Sorting of outer membrane proteins:
Mitochondrial outer membrane proteins are of two types: the transmembrane, beta-barrel porins, and the membrane-anchored, alpha-helical proteins. Beta-barrel porin precursors are translocated by the TOM complex and inserted into the outer mitochondrial membrane by the SAM complex. In contrast,...

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Related Experiment Video

Updated: Jun 24, 2026

Studying Protein Import into Chloroplasts Using Protoplasts
06:29

Studying Protein Import into Chloroplasts Using Protoplasts

Published on: December 10, 2018

Protein targeting into secondary plastids.

Kathrin Bolte1, Lars Bullmann, Franziska Hempel

  • 1Laboratory for Cell Biology, Philipps-University of Marburg, Karl-von-Frisch Strasse 8, D-35032 Marburg, Germany.

The Journal of Eukaryotic Microbiology
|April 2, 2009
PubMed
Summary

Primary plastids use most coding capacity for photosynthesis and translation. Nucleus-encoded proteins are transported post-translationally into plastids, with complex pathways for secondary plastids.

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Last Updated: Jun 24, 2026

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Published on: December 10, 2018

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Published on: September 28, 2018

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Organelle Biology

Background:

  • Primary plastids encode essential photosynthesis and translation components.
  • Most plastid proteins are nucleus-encoded and require post-translational import.
  • Plastids with more than two membranes (secondary plastids) present complex protein transport challenges.

Purpose of the Study:

  • To review recent advancements in understanding protein transport across multiple membranes in secondary plastids.
  • To elucidate the mechanisms governing protein import into complex plastid structures.

Main Methods:

  • Review of current literature on protein transport and targeting signals.
  • Analysis of data concerning nucleus-encoded protein import into plastids.
  • Comparative study of protein transport machineries in primary and secondary plastids.

Main Results:

  • Protein transport into primary plastids is crucial for essential cellular functions.
  • Secondary plastids, with up to five membranes, require intricate transport systems.
  • Existing transport mechanisms appear to be adapted for the complex needs of secondary plastids.

Conclusions:

  • Protein import into plastids is a fundamental process for cellular function.
  • The evolution of secondary plastids involved the adaptation of pre-existing protein transport pathways.
  • Understanding these pathways is key to comprehending plastid biogenesis and evolution.