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Related Concept Videos

Diffusion01:12

Diffusion

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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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Facilitated Transport01:19

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The chemical and physical properties of plasma membranes cause them to be selectively permeable. Since plasma membranes have both hydrophobic and hydrophilic regions, substances need to be able to transverse both regions. The hydrophobic area of membranes repels substances such as charged ions. Therefore, such substances need special membrane proteins to cross a membrane successfully. In  facilitated transport, also known as facilitated diffusion, molecules and ions travel across a...
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The movement of ions like sodium, potassium, and calcium into and out of the cell is essential to maintain the electrochemical gradient in living cells. The ion channels—a class of membrane transport proteins—help maintain this ionic gradient for the smooth functioning of physiological activities such as maintaining cell size and volume, conducting nerve impulses, and gas and nutrient exchange.
Ion channels are specialized integral membrane proteins on the plasma membrane that allow...
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Facilitated Transport01:19

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The chemical and physical properties of plasma membranes cause them to be selectively permeable. Since plasma membranes have both hydrophobic and hydrophilic regions, substances need to be able to transverse both regions. The hydrophobic area of membranes repels substances such as charged ions. Therefore, such substances need special membrane proteins to cross a membrane successfully. In  facilitated transport, also known as facilitated diffusion, molecules and ions travel across a...
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Aquaporins01:25

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Aquaporins or AQPs are a family of integral membrane proteins whose primary function is to transport water, while some called aquaglyceroporins also transport glycerol. In addition, aquaporins have also been suspected to be involved in transporting volatile substances, such as carbon dioxide and ammonia, across membranes. Such AQPs that act as gas channels are often highly expressed in cells involved in the gaseous exchange, such as red blood cells, epithelial cells, and pulmonary capillaries.
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Diffusion01:21

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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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Membrane Transport Processes Analyzed by a Highly Parallel Nanopore Chip System at Single Protein Resolution
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Beyond the diffusion limit: Water flow through the empty bacterial potassium channel.

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Water transport through Streptomyces lividans K+ channels is slow due to single-file ion movement. However, water can move 1,000 times faster than K+ ions, suggesting liquid-vapor oscillations in the channel.

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Area of Science:

  • Biophysics
  • Molecular Biology
  • Ion Channel Function

Background:

  • Water molecules move single-file with K+ ions in Streptomyces lividans K+ channels.
  • Understanding water transport dynamics is crucial for ion channel function.

Purpose of the Study:

  • Investigate water mobility within K+ channels.
  • Explore the mechanism behind anomalous water transport under osmotic gradients.

Main Methods:

  • Reconstitution of purified Streptomyces lividans K+ channel protein into planar bilayers.
  • Measurement of water transport kinetics under osmotic gradients.
  • Analysis of water and K+ ion interactions within the channel.

Main Results:

  • Water molecules cross the channel in <10 ps under osmotic gradients.
  • Water mobility can be 1,000x faster than K+ ion transport when K+ is removed.
  • High K+ concentrations inhibit water transport, consistent with liquid-vapor oscillations.

Conclusions:

  • Geometrical confinement in the selectivity filter drives liquid-vapor oscillations.
  • These oscillations explain anomalous water mobility and its inhibition in K+ channels.
  • Observed phenomena align with molecular dynamics simulations in hydrophobic nanopores.