Biological membrane
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2008-06-28T13:01:14Z
PhilKnight
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{{see also|Membrane}}
[[Image:Phospholipids aqueous solution structures.svg|thumb|200px|right|Cross section view of the structures that can be formed by phospholipids in aqueous solutions]]
A '''biological membrane''' or '''biomembrane''' is an enclosing or separating [[amphipathic]] layer that acts as a barrier within or around a [[cell (biology)|cell]]. It is, almost invariably, a [[lipid bilayer]], composed of a double layer of [[lipid]]-class [[molecules]], specifically [[phospholipid]]s, with occasional [[integral membrane protein|proteins]] intertwined, some of which function as [[ion channel|channels]].<ref>{{citebook|title=Neurophysiological basis of movement|author=Mark L. Latash|year=2007|id=ISBN 0736063676}}</ref>
==Function==
Such membranes typically define enclosed spaces or [[compartment]]s in which cells may maintain a [[chemistry|chemical]] or [[biochemistry|biochemical]] [[environment (biophysical)|environment]] that differs from the outside. For example, the membrane around [[peroxisome]]s shields the rest of the cell from [[peroxide]]s, and the [[plasma membrane]] separates a cell from its surrounding medium. Most [[organelle]]s are defined by such membranes, and are called '''membrane-bounded''' organelles.
Probably the most important feature of a biomembrane is that it is a [[selective permeability|selectively-permeable]] structure. This means that the size, [[electric charge|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. Biological membranes also have certain mechanical or [[Elasticity of cell membranes|elastic properties]].
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]].
== Types of biological membranes ==
* [[Cell membrane]]
* [[Mucous membrane]]
* [[S-layer]]
== See also ==
*[[Membrane lipids]]
*[[Endomembrane system]] that divides the cell into organelles
*[[Outer membrane]] or [[inner membrane]] of an organelle
*[[Biofilm]]
*[[Membrane protein]]
*[[Osmosis]]
==References==
{{refs}}
==External links==
*{{MeshName|Membranes}}
[[Category:Membrane biology| ]]
[[Category:Biological matter|membrane]]
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