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Cell membrane

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Cell membrane A cell membrane, plasma membrane or plasmalemma is a selectively permeable lipid bilayer coated by proteins which comprises the outer layer of a cell. It is a fluid patchwork of molecules in constant motion. This mobility is due to the flexible proteins and oily phospholipids that make up most of the membrane's chemical structure. Carbohydrates attached to the proteins and phospholipids form glycoproteins and glycolipids. It consists of, among other components, phospholipid and protein molecules which separate the cell interior from its surroundings within animal cells, and control the input and output of the cell through the use of receptor and cell adhesion proteins, which also play a role in cell behavior and the organization of cells within tissues. ...read more.


Rather than presenting always a formless and fluid contour, the plasma membrane surface of cells may show structure. Returning to the example of epithelial cells in the gut, the apical surfaces of many such cells are dense with involutions, all similar in size. The finger-like projections, called microvilli, increase cell surface area and facilitate the absorption of molecules from the outside. Synapses are another example of highly-structured membrane. New material is incorporated into the membrane, or deleted from it, by a variety of mechanisms. Fusion of intracellular vesicles with the membrane not only excretes the contents of the vesicle, but also incorporates the vesicle membrane's components into the cell membrane. The membrane may form blebs that pinch off to become vesicles. If a membrane is continuous with a tubular structure made of membrane material, then material from the tube can be drawn into the membrane continuously. ...read more.


In the cell membrane, phospholipid molecules create a spherical three dimensional lipid bilayer shell around the cell. A phospholipid molecule is composed of a head and two tails. The circle, or head, is the negatively charged phosphate group and the two tails are the two highly hydrophobic fatty acid chains of the phospholipid. Functions It attaches parts of the cytoskeleton to the cell membrane in order to provide shape. It attaches cells to an extra-cellular matrix in grouping cells together to form tissues. It transports molecules into and out of cells by such methods as ion pumps, channel proteins and carrier proteins. It acts as receptor for the various chemical messages that pass between cells such as nerve impulses and hormone activity. It takes part in enzyme activity which can be important in the metabolism or as part of the body's defense mechanism. ...read more.

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