membran

'''Definition'''

''noun''

(cell biology)

The [[outer]] covering of the [[cell]] consisting of a lipid bilayer with proteins embedded in it.


'''Supplement'''

Although some [[cell]]s form another layer above the cell membrane (called [[cell wall]]), other [[cells]] have the cell membrane as the only [[protective]] [[barrier]] between the [[cytoplasm]] and the outside of the [[cell]].

The cell membrane is a [[phospholipid]] bilayer interspersed with [[proteins]] as depicted in the [[Fluid Mosaic Model]]. Its structure and composition makes it selectively [[permeable]] (or semipermeable), which means not every [[substance]] is allowed to enter or leave the [[cell]]. The cell membrane controls which substances can go in and out of the cell. It can allow a particular substance to pass through at a certain time, and then reject the same substance at a later time.

Its other main functions include [[cell adhesion]], [[ion]] [[channel]] conductance, [[cell]] signaling, and [[attachment]] point for [[cytoskeleton]] (which is important in keeping the shape of the cell).

Another interesting feature of the cell membrane is the presence of [[surface]] [[molecule]]s (e.g. [[glycoprotein]]s, glycolipids, etc.) that act like a ‘signature’ for a cell. Every cell has a different ‘signature’ or ‘marker’ that is thought to function in [[cell recognition]], or in a sort of cellular identification system.



Related forms: cellular membrane.

Synonym: [[plasma membrane]], [[plasmalemma]], [[cytomembrane]].

See also: [[cell]], [[organelle]].