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Encyclopedia > Biological membrane
See also: Membrane

A biological membrane or biomembrane is an enclosing or separating tissue which acts as a barrier within or around a cell. It is, almost invariably, a lipid bilayer (except for Archaea which have isoprene membranes), composed of a double layer of lipid-class molecules, specifically phospholipids, with occasional proteins intertwined, some of which function as channels. Image File history File links Information_icon. ... It has been suggested that Net flux be merged into this article or section. ... Drawing of the structure of cork as it appeared under the microscope to Robert Hook from Micrographia which is the origin of the word cell. Cells in culture, stained for keratin (red) and DNA (green). ... A diagonal molecular slab from the DPPC lipid bilayer simulation1; color scheme: PO4 - green, N(CH3)3 - violet, water - blue, terminal CH3 - yellow, O - red, glycol C - brown, chain C - grey. ... Phyla / Classes Phylum Crenarchaeota Phylum Euryarchaeota     Halobacteria     Methanobacteria     Methanococci     Methanopyri     Archaeoglobi     Thermoplasmata     Thermococci Phylum Korarchaeota Phylum Nanoarchaeota Archaea (; from Greek αρχαία, old ones; singular Archaeum, Archaean, or Archaeon), also called Archaebacteria (), is a major division of living organisms. ... Isoprene is a common synonym for the chemical compound 2-methyl-1,3-butadiene. ... Lipids are a class of hydrocarbon-containing organic compounds. ... In science, a molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ... Two schematic representations of a phospholipid. ... An Integral Membrane Protein (IMP) is a protein molecule (or assembly of proteins) that is permanently attached to the biological membrane. ... Ion channels are pore-forming proteins that help to establish and control the small voltage gradient that exists across the plasma membrane of all living cells (see cell potential) by allowing the flow of ions down their electrochemical gradient. ...


Such membranes typically define enclosed spaces or compartments in which cells may maintain a chemical or biochemical environment that differs from the outside. For example, the membrane around peroxisomes shields the rest of the cell from peroxides, and the plasma membrane separates a cell from its surrounding medium. Most organelles are defined by such membranes, and are called membrane-bound organelles. In heraldry, a compartment is a design placed under the shield, usually rocks, a grassy mount, or some sort of other landscape upon which the supporters are depicted as standing (a compartment without supporters is possible but practically unknown, with the exception of South Australia[1]). It is sometimes said... Chemistry (from Greek χημεία khemeia[1] meaning alchemy) is the science of matter at the atomic to molecular scale, dealing primarily with collections of atoms, such as molecules, crystals, and metals. ... Biochemistry is the study of the chemical processes and transformations in living organisms. ... Basic structure of a peroxisome Peroxisomes are ubiquitous organelles in eukaryotes that function to rid the cell of toxic substances. ... Peroxide has three distinct meanings: // Main article: hydrogen peroxide In common usage, peroxide is an aqueous solution of hydrogen peroxide (HOOH or H2O2) sold for use as a disinfectant or mild bleach. ... Drawing of a cell membrane A component of every biological cell, the cell membrane (or plasma membrane) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. ... Schematic of typical animal cell, showing subcellular components. ...


Probably the most important feature of a biomembrane is that it is a selectively permeable structure. This means that the size, charge and other chemical properties of the atoms and molecules attempting to cross it will determine whether they succeed to do so. Selective permeability is essential for effective separation of a cell or organelle from its surroundings. Partially permeable is a biological term which describes the characteristic of a barrier to selectively allow substances to pass through. ... Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interactions. ... Wikipedia does not yet have an article with this exact name. ... Properties For alternative meanings see atom (disambiguation). ...


If a particle is too large or otherwise unable to cross the membrane by itself, but is still needed by a cell, it could either go through one of the protein channels, or be taken in by means of endocytosis. Endocytosis is a process whereby cells absorb material (molecules such as proteins) from the outside by engulfing it with their cell membrane. ...

Contents

Types of biological membranes

Illustration of a lipid bilayer The cell membrane, also called the plasma membrane or plasmalemma and cell surface membrane, is a selectively permeable lipid bilayer which comprises the outer layer of a cell. ... The mucous membranes (or mucosae; singular: mucosa) are linings of ectodermic origin, covered in epithelium, and are involved in absorption and secretion. ... An S-layer is a membrane commonly found in gram-positive and gram-negative bacteria, as well as among Archaea. ...

Structure

yes


Composition

The three major classes of membrane lipids are phospholipids, glycolipids, and cholesterol. Two schematic representations of a phospholipid. ... Glycolipids are carbohydrate-attached lipids. ... Cholesterol is a sterol (a combination steroid and alcohol) and a lipid found in the cell membranes of all body tissues, and transported in the blood plasma of all animals. ...

The major membrane lipidsPtdCho - Phosphatidylcholine; PtdEtn - Phosphatidylethanolamine; PtdIns - Phosphatidylinositol; PtdSer - Phosphatidylserine.
The major membrane lipids
PtdCho - Phosphatidylcholine; PtdEtn - Phosphatidylethanolamine; PtdIns - Phosphatidylinositol; PtdSer - Phosphatidylserine.

Phospholipids and glycolipids consist of two long, nonpolar (hydrophobic) hydrocarbon chains linked to a hydrophilic head group. In the phospholipids the head consist of phosphorylated either: Image File history File links Download high-resolution version (579x607, 10 KB) I, the creator of this work, hereby release it into the public domain. ... Image File history File links Download high-resolution version (579x607, 10 KB) I, the creator of this work, hereby release it into the public domain. ...

  • Glycerol (and hence the name phosphoglycerides given to this group of lipids).
  • Sphingosine (with only one member - sphingomyelin).

In the glycolipids the head contains of sphingosine with one or several sugar units attached to it. The hydrophobic chains belong either to: Sphingomyelin is a type of sphingolipid found in animal cell membranes, especially in the membranous myelin sheath which surrounds some nerve cell axons. ...

  • two fatty acids - in the case of the phosphoglycerides.
  • one FA and the hydrocarbon tail of sphingosine - in the case of sphingomyelin and the glycolipids.

The FAs in phospho- and glycolipids usually contain an even number of carbon atoms, typically between 14 and 24. The 16- and 18-carbon FAs are the most common ones. FAs may be saturated or unsaturated, with the configuration of the double bonds nearly always cis. The length and the degree of unsaturation of FAs chains have a profound effect on membranes fluidity. In chemistry, especially biochemistry, a fatty acid is a carboxylic acid often with a long unbranched aliphatic tail (chain), which is either saturated or unsaturated. ... Sphingosine is a compound that forms a primary part of the sphingolipids, a class of cell membrane lipids which includes sphingomyelin, an important phospholipid. ...


In phosphoglycerides, the hydroxyl groups at C-1 and C-2 of glycerol are esterified to the carboxyl groups of the FAs. The C-3 hydroxyl group is esterified to phosphoric acid. The resulting compound, called phosphatidate, is the simplest phosphoglycerate. Only small amounts of phosphatidate are present in membranes. However, it is a key intermediate in the biosynthesis of the other phosphoglycerides. Phosphatidate (red: phosphate group, blue & green: fatty acid) Phosphatidates are biochemical compounds that consist of a glycerol backbone, with a (usually) saturated fatty acid bonded to carbon-1, a (usually) unsaturated fatty acid bonded to carbon-2 and a phosphate group bonded to carbon-3. ...


Sphingosine is an amino alcohol that contains long, unsaturates hydrocarbon chain. In sphingomyelin and glycolipids, the amino group of sphingosine is linked to a FAs by an amid bond. In sphingomyelin the primary hydroxyl group of sphingosine is esterified to phosphoryl choline. In glycolipids, the sugar component is attached to this group. The simplest glycolipid is cerebroside, in which there is only one sugar residue, either Glc or Gal. More complex glycolipids, such as gangliosides, contain a branched chain of as many as seven sugar residues. // Choline is a nutrient, essential for cardiovascular and brain function, and for cellular membrane composition and repair. ... Cerebrosides are glycosphingolipids which are important components in animal muscle and nerve cell membranes. ... Glucose (Glc), a monosaccharide (or simple sugar), is the most important carbohydrate in biology. ... Galactose (also called brain sugar) is a type of sugar found in dairy products, in sugar beets and other gums and mucilages. ... Ganglioside is a compound composed of a glycosphingolipid (ceramide and oligosaccharide) with one or more sialic acids (AKA n-acetylneuraminic acid) linked on the sugar chain. ...


See also

Staphylococcus aureus biofilm on an indwelling catheter. ... A membrane protein is a protein molecule that is attached to, or associated with the membrane of a cell or an organelle. ... Osmosis is the movement of water through a selectively permeable membrane from a region of low solute potential to a region of high solute potential (or equivalently, from a region of high solvent potential to a region of low solvent potential). ...

External links

  • Membrane receptors (Animation)

  Results from FactBites:
 
Cell membrane - Wikipedia, the free encyclopedia (830 words)
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.
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.
Biological membrane - Wikipedia, the free encyclopedia (252 words)
A biological membrane or biomembrane is a membrane which acts as a barrier within or around a cell.
It is, almost invariably, a lipid bilayer (except for Archaea which have isoprene membranes), being composed of a double layer of lipid-class molecules, specifically phospholipids, with occasional proteins intertwined, some of which function as channels.
For example, the membrane around peroxisomes shields the rest of the cell from peroxides, and the plasma membrane separates a cell from its surrounding medium.
  More results at FactBites »

 
 

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