Structure and function of plasma membrane

Most hydrophilic, or water-soluble, substances are repelled by this hydrophobic interior and cannot simply diffuse through the membrane. Instead, these substances must cross the membrane using specialized transport mechanisms. Examples of lipid-insoluble substances that require such mechanisms include nutrient molecules, such as glucose and amino acids, and all species of ions (Na+, Ca++, H+, Cl, and HC03). Therefore, the plasma membrane plays a very important role in determining the composition of the intracellular fluid by selectively permitting substances to move in and out of the cell. 

Pharmacy application lipid solubility and drug elimination 

Proteins are also associated with the lipid bilayer and essentially float within it. Intrinsic proteins are embedded within and span the membrane, and extrinsic proteins are found on the internal or external surface of the 

The plasma membrane contains a small amount of carbohydrate (2 to 10% of the mass of the membrane) on the outer surface. This carbohydrate is found attached to most of the protein molecules, forming glycoproteins, and to some of the phospholipid molecules ( 10%), forming glycolipids. Consequently, the external surface of the cell has a carbohydrate coat, or glycocalyx. 

These carbohydrate moieties have several important functions, including  

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