Sztul, Elizabeth Department of Cell Biology, University of Alabama, Birmingham, Alabama.
Last reviewed:April 2019
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- Membrane structure and composition
- Membrane functions
- Membrane biogenesis
- Membrane disease
- Links to Primary Literature
- Additional Readings
Any of the thin semipermeable layers of protoplasm, consisting mainly of lipids and proteins, which are present on the surface of all cells. Cells maintain their content separate and distinct from the external environment by a semifluid lipid bilayer, that is, a cell membrane (often referred to as the plasma membrane or plasmalemma) [Fig. 1], which prevents the free exchange of most biological molecules and acts as a barrier between the inside and the outside of a cell. Prokaryotic cells contain only one such membrane, the plasma membrane, which delineates the border of the cell. Eukaryotic cells contain, in addition to the plasma membrane, a multitude of internal membranes that define distinct intracellular organelles. The role of the plasma membrane and the internal membranes is analogous—all prevent the free exchange of molecules between the inside and the outside of the enclosed compartment, thus allowing the generation and maintenance of specialized microenvironments within each membrane-enclosed space. See also: Cell (biology); Cell organization; Lipid; Lipid rafts (membranes); Protein
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