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Topic: Membrane


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  membrane. The Columbia Encyclopedia, Sixth Edition. 2001-05
Membrane organization is based on a sheet two molecules thick—a double layer of lipids aligned with their long hydrocarbon tails tucked inside—studded with protein molecules, some of which extend completely through the lipid bilayer.
The basic function of the membrane is to provide for the integrity of the cell—e.g., to separate the outside from the inside.
In this case, specific membrane proteins called receptors bind hormones or other such informational molecules and subsequently transmit a signal to the interior of the cell.
www.bartleby.com /65/me/membrane.html   (265 words)

  
  Cell Membranes   (Site not responding. Last check: 2007-10-29)
The plasma membrane serves as the interface between the machinery in the interior of the cell and the extracellular fluid (ECF) that bathes all cells.
Phospholipids are amphiphilic with the hydrocarbon tail of the molecule being hydrophobic; its polar head hydrophilic.
Membrane proteins are often restricted in their movements.
users.rcn.com /jkimball.ma.ultranet/BiologyPages/C/CellMembranes.html   (446 words)

  
  Extracorporeal Membrane Oxygenation (ECMO), Cincinnati Children's Hospital Medical Center   (Site not responding. Last check: 2007-10-29)
Extracorporeal Membrane Oxygenation is the use of an artificial lung (membrane) located outside the body (extracorporeal), that puts oxygen into the blood and then carries this blood to the body tissues (oxygenation).
When initiated in the operating room, the tubes connecting the patient to the extracorporeal membrane oxygenation circuit are generally placed directly into the large blood vessels adjacent to the heart, similar to the connections made during open heart surgery.
With extracorporeal membrane oxygenation, survival in these situations is reported to improve to between 20 percent to 60 percent depending on the specific circumstances.
www.cincinnatichildrens.org /health/heart-encyclopedia/treat/surg/ecmo.htm   (874 words)

  
  Cell membrane - Encyclopedia.WorldSearch   (Site not responding. Last check: 2007-10-29)
The basic composition and structure of the plasma membrane is the same as that of the membranes that surround organelles and other subcellular compartments.
The foundation is a phospholipid bilayer, and the membrane as a whole is often described as a 'fluid mosaic' - a two-dimensional fluid of freely diffusing lipids, dotted or embedded with proteins which may function as channels or transporters across the membrane, or as receptors.
Passive transport is a means of moving different chemical substances across membranes through diffusion of hydrophobic (non polar) and small polar molecules, or facilitated diffusion of polar and ionic molecules, which relies on a transport protein to provide a channel or bind to specific molecules.
encyclopedia.worldsearch.com /cell_membrane.htm   (859 words)

  
 Structure of the Plasma Membrane
The outer leaflet of the plasma membrane consists mainly of phosphatidylcholine and sphingomyelin, whereas phosphatidylethanolamine and phosphatidylserine are the predominant phospholipids of the inner leaflet.
The hydrophobic portions of detergents displace the membrane lipids and bind to the hydrophobic portions of integral membrane proteins.
Membrane proteins and phospholipids are unable to move back and forth between the inner and outer leaflets of the membrane at an appreciable rate.
www.ncbi.nlm.nih.gov /books/bv.fcgi?rid=cooper.section.1967   (3093 words)

  
 Cell membrane - Wikipedia, the free encyclopedia
A component of every biological cell, the selectively permeable cell membrane (or plasma membrane or plasmalemma) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell.
The foundation is a phospholipid bilayer, and the membrane as a whole is often described as a fluid mosaic – a two-dimensional fluid of freely diffusing lipids, dotted or embedded with proteins which may function as channels or transporters across the membrane, or as receptors.
Some of these proteins simply adhere to the membrane (extrinsic or peripheral proteins), while others might be said to reside within it or to span it (intrinsic proteins – more at integral membrane protein).
en.wikipedia.org /wiki/Cell_membrane   (830 words)

  
 Cell Membrane   (Site not responding. Last check: 2007-10-29)
The outer cell membrane and the membranes surrounding inner cell organelles are bilipid layers.
The membrane is approximately 5 nanometres thick.(a nanometre is a billionth of a metre thick)
Membrane proteins diffuse throughout the membrane in the same fashion, though at a slower pace because of their relatively massive size compared to a phospholipid molecule.
www.jdaross.mcmail.com /cell2.htm   (1070 words)

  
 UCMP Glossary: Cell biology
The cell consists primarily of an outer plasma membrane, which separates it from the environment; the genetic material (DNA), which encodes heritable information for the maintainance of life; and the cytoplasm, a heterogeneous assemblage of ions, molecules, and fluid.
Plants are known for their cell walls of cellulose, as are the green algae and certain protists, while fungi have cell walls of chitin.
This is believed to be the result of endosymbiosis, with the outer membrane coming from the eukaryotic cell, and the inner membrane belonging to the original prokaryote which was "swallowed".
www.ucmp.berkeley.edu /glossary/gloss4cell.html   (1470 words)

  
 Membrane Structure and Function
Membranes are vital because they separate the cell from the outside world.
Cellular membranes have diverse functions in the different regions and organelles of a cell.
Plasma membranes of human red blood cells and mouse liver contain nearly equal amounts of proteins (44, 49% respectively) and lipids (43, 52% respectively).
cellbio.utmb.edu /cellbio/membrane_intro.htm   (1761 words)

  
 Membrane Proteins
Associated with each membrane is a set of membrane proteins that enables the membrane to carry out its distinctive activities (Figure 3-32).
Peripheral proteins localized to the cytosolic face of the plasma membrane include the cytoskeletal proteins spectrin and actin in erythrocytes (Chapter 18) and the enzyme protein kinase C. This enzyme shuttles between the cytosol and the cytosolic face of the plasma membrane and plays a role in signal transduction (Chapter 20).
When the polypeptide chain of a transmembrane protein spans the membrane multiple times, the core of the protein generally is hydrophilic, permitting passage of water-soluble molecules, and the surface is hydrophobic, permitting interaction with the interior of the lipid bilayer.
www.ncbi.nlm.nih.gov /books/bv.fcgi?call=bv.View..ShowSection&rid=mcb.section.608   (1985 words)

  
 eMedicine - Epimacular Membrane : Article by Bradley M Hughes, MD
Membranes associated with retinal breaks, previous retinal detachments, or cryopexy are composed mainly of dispersed RPE cells, while cells of glial origin predominate in the IEMM.
As the membrane progresses, the visual disturbance is often vague and difficult for the patient to describe.
Membranes causing an irregular wrinkling of the inner retinal surface are classified as grade 1 EMMs.
www.emedicine.com /oph/topic396.htm   (2978 words)

  
 Membrane - Wikipedia, the free encyclopedia
A membrane is a thin, typically planar structure or material that separates two environments.
Because it sits between environments or phases and has a finite volume, it can be referred to as an interphase rather than an interface.
Membranes selectively control mass transport between the phases or environments.
en.wikipedia.org /wiki/Membrane   (88 words)

  
 1.1 Membrane Structure and Composition   (Site not responding. Last check: 2007-10-29)
This is known as the fluid mosaic model of biological membranes (mosaic because it includes proteins, cholesterol, and other types of molecules besides phospholipids).
Membrane proteins diffuse throughout the membrane in the same fashion, though at a slower pace because of their massive size (a phospholipid may be 650 d (daltons, or MW), and a medium sized protein can be 100,000 d).
Another way for the cell to control the fluidity of its membrane is to regulate the ratio of saturated to unsaturated hydrocarbon chains of the phospholipids.
web.mit.edu /esgbio/www/cb/membranes/structure.html   (512 words)

  
 AllRefer.com - membrane (Cell Biology) - Encyclopedia
membrane, structure composed mostly of lipid and protein that forms the external boundary of cells and of major structures within cells.
Membrane organization is based on a sheet two molecules thick : a double layer of lipids aligned with their long hydrocarbon tails tucked inside : studded with protein molecules, some of which extend completely through the lipid bilayer.
The basic function of the membrane is to provide for the integrity of the cell : e.g., to separate the outside from the inside.
reference.allrefer.com /encyclopedia/M/membrane.html   (319 words)

  
 THE CELL MEMBRANE HEADQUARTERS
Sometimes carbohydrates (sugars) are attached to cell membrane phospholipids and to cell membrane proteins.
Functionally the cell membrane serves as both a gateway and a barrier for the cell.
The cell membrane is composed of phospholipids and proteins.
www.usd.edu /~bgoodman/Membrane.htm   (540 words)

  
 CiteULike: Characteristics of a membrane reservoir buffering membrane tension.   (Site not responding. Last check: 2007-10-29)
Characteristics of a membrane reservoir buffering membrane tension.
During the major elongation phase, tether force is constant, buffered by the "membrane reservoir." Finally, there is an abrupt exponential rise in force that brings the tether out of the trap, indicating depletion of the membrane reservoir.
Thus, we suggest that cells maintain a plasma membrane reservoir to buffer against changes in membrane tension and that the reservoir is increased with membrane tension or disruption of the cytoskeleton.
www.citeulike.org /user/tsjipko/article/802702   (704 words)

  
 Fueling the hydrogen future with Argonne's ceramic membrane
Though the membranes currently used for research are only a few millimeters across, once scaled up for industrial use, they could be installed at existing refineries or at individual refueling stations.
Ceramic membranes, such as Argonne's new hydrogen membrane, are made of dense, conductive materials that only allow electrons and certain ions, or charged atoms, to pass through.
Charged hydrogen particles pass through the membrane, and the resulting pure hydrogen that emerges from the other side is captured for immediate use, storage or transport.
www.eurekalert.org /features/doe/2004-06/dnl-fth061404.php   (993 words)

  
 Membrane Biophysics
Membranes and membrane proteins have become an important focus of the current efforts in structural genomics.
Membrane proteins represent a significant fraction of the proteins expressed by a cell (30 to 40%), yet less than one-half of one percent of the structures that have been deposited in the protein data bank are membrane proteins.
Membrane fusion is a ubiquitous biological process that functions in the release of neurotransmitters, secretion and viral infection; yet, it remains one of the key unsolved problems in membrane biophysics and cell biology.
www.healthsystem.virginia.edu /internet/bims_scbb/membiop.cfm   (868 words)

  
 MEMBRANES
Membranes separate and maintain the chemical environments of the two sides of the membrane.
The beta-subunit is a glycoprotein, with the carbohydrate on the external surface of the membrane.
The receptor-insulin complex migrates to a region of the plasma membrane with the protein clathrin coating its inner surface.
www-medlib.med.utah.edu /NetBiochem/membrane.htm   (2845 words)

  
 membrane on Encyclopedia.com
Membrane organization is based on a sheet two molecules thick—a double layer of lipids aligned with their long hydrocarbon tails tucked inside—studded with protein molecules, some of which extend completely through the lipid bilayer.
Downregulation of fibronectin overexpression reduces basement membrane thickening and vascular lesions in retinas of galactose-fed rats.
This membrane electron assembly is the functional heart of the fuel cell.
www.encyclopedia.com /html/m1/membrane.asp   (850 words)

  
 Membrane potentials
Membrane potentials are determined primarily by three factors: 1) the concentration of ions on the inside and outside of the cell; 2) the permeability of the cell membrane to those ions (i.e., ion conductance); and 3) by the activity of electrogenic pumps (e.g., Na
At a resting membrane potential of -90 mV, there is a very large electrical and chemical driving force (-140 mV) acting upon external Na to cause these ions to diffuse into the cell.
However, to fully understand how multiple ions affect the membrane potential, and ultimately how the membrane potential changes during action potentials, it is necessary to learn how changes in membrane ion permeability, that is, changes in ion conductance, affect the membrane potential.
www.cvphysiology.com /Arrhythmias/A007.htm   (765 words)

  
 Membrane Plugin, Version 1.1
Many of these molecules are membrane proteins, which function may (and often does) critically depend on the structure of the surrounding lipid membrane.
The distance between the layers was set to fit the actual membrane thickness, and the lattice period was set to fit the actual surface density of lipid molecules.
Load the both protein and membrane into VMD and align the protein to the proper position and orientation in the membrane.
www.ks.uiuc.edu /Research/vmd/plugins/membrane   (681 words)

  
 The Cell Membrane
To perform the function of the organelle, the membrane is specialized in that it contains specific proteins and lipid components that enable it to perform its unique roles for that cell or organelle.
In essence membranes are essential for the integrity and function of the cell.
Membranes help organize the cell into domains and microdomains.
cellbio.utmb.edu /cellbio/membrane.htm   (412 words)

  
  American Water Works Association   (Site not responding. Last check: 2007-10-29)
Membrane filtration is becoming a common technology used to treat municipal drinking water.
Membrane technology is rapidly gaining acceptance throughout the world as an effective and economical water treatment method.
A membrane is a thin layer of material that separates substances when a driving force is applied across the membrane.
www.awwa.org /Advocacy/pressroom/MembraneFiltration.cfm   (355 words)

  
 Circular Membrane Modes
The preferred vibrational modes for a timpani are a subset of the modes of a circular membrane.
The vibrational modes of a circular membrane are very important musically because of drums, and in particular the timpani.
The expression for the fundamental frequency of a circular membrane has some similarity to that for a stretched string, in that it depends on tension and density.
hyperphysics.phy-astr.gsu.edu /hbase/music/cirmem.html   (193 words)

  
 Membrane Proteins   (Site not responding. Last check: 2007-10-29)
Extrinsic membrane proteins are entirely outside of the membrane, but are bound to it by weak molecular attractions (ionic, hydrogen, and/or Van der Waals bonds).
Intrinsic membrane proteins, the class we are mainly interested in, are embedded in the membrane.
Cells contain proteins that are embedded in the lipid bilayer of their plasma membranes and extend from one side of the membrane through to the other.
web.mit.edu /esgbio/www/cb/membranes/proteins.html   (559 words)

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