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Related Concept Videos

Diffusion01:12

Diffusion

226.7K
Diffusion is the passive movement of substances down their concentration gradients—requiring no expenditure of cellular energy. Substances, such as molecules or ions, diffuse from an area of high concentration to an area of low concentration in the cytosol or across membranes. Eventually, the concentration will even out, with the substance moving randomly but causing no net change in concentration. Such a state is called dynamic equilibrium, which is essential for maintaining overall...
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Diffusion01:21

Diffusion

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Diffusion is a type of passive transport. In passive transport, a substance tends to move from an area of high concentration to an area of low concentration until the concentration is equal across the space. For example, take the diffusion of substances through the air. When someone opens a perfume bottle in a room filled with people, the perfume is at its highest concentration in the bottle and is at its lowest at the edges of the room. The perfume vapor will diffuse, or spread away, from the...
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Protein Diffusion in the Membrane01:24

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Proteins show rotational as well as lateral diffusion across the membrane. The lateral diffusion of proteins was confirmed through the cell fusion experiment where mouse and human cells were fused, resulting in hybrid cells. When the human and mouse cells fused, the specific membrane proteins on human and mouse cells were marked with the red and green-fluorescent markers, respectively. Initially, the red and green fluorescence was located on the respective hemisphere of the cell. As time...
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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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Passive Diffusion: Overview and Kinetics01:17

Passive Diffusion: Overview and Kinetics

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Passive diffusion is a critical process that allows small lipophilic drugs to cross the cell membrane along a concentration gradient. This mechanism's efficiency depends on four primary factors: the membrane's surface area, the drug's lipid-water partition coefficient, the concentration gradient, and the membrane's thickness.
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Behavior of Gas Molecules: Molecular Diffusion, Mean Free Path, and Effusion03:48

Behavior of Gas Molecules: Molecular Diffusion, Mean Free Path, and Effusion

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Although gaseous molecules travel at tremendous speeds (hundreds of meters per second), they collide with other gaseous molecules and travel in many different directions before reaching the desired target. At room temperature, a gaseous molecule will experience billions of collisions per second. The mean free path is the average distance a molecule travels between collisions. The mean free path increases with decreasing pressure; in general, the mean free path for a gaseous molecule will be...
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Related Experiment Video

Updated: Mar 9, 2026

Single-Molecule Tracking Microscopy - A Tool for Determining the Diffusive States of Cytosolic Molecules
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Molecular Diffusion through Cyanobacterial Septal Junctions.

Mercedes Nieves-Morión1, Conrad W Mullineaux2, Enrique Flores3

  • 1Instituto de Bioquímica Vegetal y Fotosíntesis, Consejo Superior de Investigaciones Científicas and Universidad de Sevilla, Seville, Spain.

Mbio
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Summary

Heterocyst-forming cyanobacteria use septal junctions for intercellular molecular transfer, which occurs via simple diffusion, similar to metazoan gap junctions. This finding reveals a novel diffusion mechanism for bacterial cytoplasmic membranes.

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Area of Science:

  • Microbiology
  • Cell Biology
  • Biophysics

Background:

  • Heterocyst-forming cyanobacteria exhibit multicellular behavior with intercellular communication.
  • Molecular exchange between cells in these filaments is crucial for nutrient sharing and differentiation.
  • Septal junctions are hypothesized mediators of this intercellular transfer.

Purpose of the Study:

  • To investigate the mechanism and temperature dependence of intercellular molecular transfer in cyanobacteria.
  • To determine if molecular exchange through septal junctions follows simple diffusion or requires an activated process.
  • To compare the function of cyanobacterial septal junctions to known intercellular communication structures.

Main Methods:

  • Utilized fluorescence recovery after photobleaching (FRAP) assays.
  • Employed fluorescent markers (e.g., calcein, 5-carboxyfluorescein, esculin) to trace molecular movement.
  • Studied the model organism Anabaena sp. strain PCC 7120.

Main Results:

  • Intercellular transfer rate constants were found to be directly proportional to absolute temperature.
  • The observed transfer kinetics align with the physical properties of simple diffusion.
  • Cyanobacterial septal junctions facilitate rapid, non-selective exchange of small molecules.

Conclusions:

  • Cyanobacterial septal junctions enable molecular exchange through simple diffusion, a novel mechanism for bacterial membranes.
  • These junctions are functionally analogous to metazoan gap junctions.
  • This discovery expands the understanding of molecular transfer mechanisms in prokaryotes.