1.3 14BCell Membrane
The cell membrane separates the interior of the cell from the outside environment [15].
Cell membrane is the first part of cell which comes in contact with any nutrients, pathogen, or
other molecules present in cellular environment. So understanding the cell membrane is of
tremendous biological importance. Biological membranes are uniquely capable of a variety of
functions due to the intrinsic properties of the membrane structure. For example, membranes are
generally semi-permeable [16]. That is, most molecules cannot penetrate inside the membrane
unless proteins facilitate their movement. This property allows the membranes of a cell to control
the passage of materials moving across the cell membrane. Biological membranes contains a
wide variety of molecules, primarily lipids and proteins; other constituents include: water,
cholesterol, sugar groups, metal ions and carbohydrates [17] (see Fig 1.1). Cholesterol is not
found in all types of membranes.
The lipid molecules in cell membrane are spontaneously arrange themselves so that non-
polar, hydrophobic fatty acid tail regions are shielded from the surrounding polar fluid, causing
the hydrophilic head region to associate with the cytosolic and extracellular faces of the resulting
bilayer. The proteins usually span from one side of the phospholipids bilayer to the other
(integral proteins), but can also sit on one of the surfaces (peripheral proteins). The peripheral
proteins can slide around the membrane very quickly and collide with each other, but can never
flip from one side to the other. The extracellular surface of the cell membrane is decorated
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1.3 14BCell Membrane The cell membrane separates the interior of the cell from the outside environment [15]. Cell membrane is the first part of cell which comes in contact with any nutrients, pathogen, or other molecules present in cellular environment. So understanding the cell membrane is of tremendous biological importance. Biological membranes are uniquely capable of a variety of functions due to the intrinsic properties of the membrane structure. For example, membranes are generally semi-permeable [16]. That is, most molecules cannot penetrate inside the membrane unless proteins facilitate their movement. This property allows the membranes of a cell to control the passage of materials moving across the cell membrane. Biological membranes contains a wide variety of molecules, primarily lipids and proteins; other constituents include: water, cholesterol, sugar groups, metal ions and carbohydrates [17] (see Fig 1.1). Cholesterol is not found in all types of membranes. The lipid molecules in cell membrane are spontaneously arrange themselves so that non-polar, hydrophobic fatty acid tail regions are shielded from the surrounding polar fluid, causing the hydrophilic head region to associate with the cytosolic and extracellular faces of the resulting bilayer. The proteins usually span from one side of the phospholipids bilayer to the other (integral proteins), but can also sit on one of the surfaces (peripheral proteins). The peripheral proteins can slide around the membrane very quickly and collide with each other, but can never
flip from one side to the other. The extracellular surface of the cell membrane is decorated
7
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