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The cell Membrana This basic cell membrane structure has some very important features. It is fluid in nature allowing cell mobility. Note as mentioned above the
Submitted by lil_miss_ugo on June 6, 2006
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This basic cell membrane structure has some very important features. It is fluid in nature allowing cell mobility. Note as mentioned above the physical properties of the bilipid layer mean that left to itself the shape of the cell will be spherical. However the fluid nature of the membrane means that the huge variety in cell shapes found in nature is possible. This bilipid layer is variably permeable, meaning that some molecules are allowed to pass freely (diffuse) through the membrane. The lipid bilayer is virtually impermeable to large molecules, relatively impermeable to molecules as small as charged ions such as Na+ and K+, and quite permeable to lipid soluble low molecular weight molecules such as ethanol (the organic chemical which gives alcoholic beverages their properties). The layer is extremely permeable to water molecules, but it is not well understood why. Molecules that can diffuse through the membrane do so at differing rates depending upon their ability to enter the hydrophobic interior of the membrane bilayer. Any breaks or ruptures of the cell membrane are spontaneously repaired due to the molecular properties of the bilipid layer wanting to eliminate any free edges when in contact with water. Studded throughout or associated with the bilipid layer there are various membrane proteins, which perform various functions such as enzyme activity, cell attachment, communicating with other cells and transport various substances into and out of the cell.
The Fluid Mosaic Model
Lipid bilayers are fluid, and individual phospholipids diffuse rapidly throughout the two dimensional surface of the membrane. This is known as the fluid mosaic model of biological membranes (mosaic because it includes proteins, cholesterol, and other types of molecules besides phospholipids). The phospholipids can move to the opposite side of a bacterial cell membrane in a few minutes at room temperature. That is a distance several thousand times the size of the...
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