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Related Concept Videos

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...
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 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...
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.
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.
Photosystems01:32

Photosystems

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 molecules...

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Updated: Jun 19, 2026

Studying the Supramolecular Organization of Photosynthetic Membranes within Freeze-fractured Leaf Tissues by Cryo-scanning Electron Microscopy
13:52

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

Published on: June 23, 2016

Protonation and chloroplast membrane structure.

S Murakami1, L Packer

  • 1Department of Physiology-Anatomy, University of California, Berkeley, California 94720.

The Journal of Cell Biology
|October 30, 2009
PubMed
Summary
This summary is machine-generated.

Light causes chloroplasts to contract by altering thylakoid structure and membrane thickness. This structural change is linked to protonation and osmotic shifts within the chloroplast membranes.

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Studying Protein Import into Chloroplasts Using Protoplasts
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Last Updated: Jun 19, 2026

Studying the Supramolecular Organization of Photosynthetic Membranes within Freeze-fractured Leaf Tissues by Cryo-scanning Electron Microscopy
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Studying Protein Import into Chloroplasts Using Protoplasts
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Studying Protein Import into Chloroplasts Using Protoplasts

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Area of Science:

  • Plant Biology
  • Cellular Biology
  • Biophysics

Background:

  • Chloroplasts are vital organelles for photosynthesis in plant cells.
  • Light is known to induce structural changes within chloroplasts, but the precise mechanisms remain under investigation.

Purpose of the Study:

  • To investigate the structural alterations in chloroplasts induced by light.
  • To elucidate the sequence of events and underlying mechanisms driving these light-induced structural changes.

Main Methods:

  • High-resolution electron microscopy
  • Photometric methods (microdensitometry, light scattering, transmission)
  • Chemical modification and fluorescence analysis (anilinonaphthalene sulfonic acid)

Main Results:

  • Illumination causes reversible chloroplast membrane contraction, thylakoid flattening, and decreased membrane spacing.
  • A 13-23% decrease in membrane thickness was observed upon illumination or H+ addition, suggesting an osmotic mechanism.
  • Light scattering changes correlate with membrane thickness/conformation, while transmission changes relate to spacing and osmotic effects.
  • Fluorescence changes preceded light scattering and transmission alterations, indicating early molecular events.

Conclusions:

  • Light-induced structural changes in chloroplasts involve a cascade starting with protonation and membrane environment shifts.
  • These lead to changes in membrane thickness and internal osmolarity, causing thylakoid collapse and altered chloroplast morphology.
  • The findings provide a detailed temporal sequence for light-induced chloroplast structural dynamics.