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Before discussing what characteristic of phospholipids is important to their function?, I would like to define what phospholipids are. Phospholipids are the most abundant type of lipids mainly found in the cell membrane and membranes of different organelles.
If you look at the classification of lipids, there are two main class of the lipids; saponifiable lipids and non-saponifiable lipids. Saponifiable lipids can be further divided into two subclasses; glycerol esters and non-glycerol esters. Therefore, phospholipids are a type of glycerol esters. In a glycerol molecule, the first and second hydroxyl-O atoms are linked to two free fatty acid residues through an ester linkage, while the last (third) hydroxyl-O atom is linked to a phosphate group through a phosphoester bond.
Yes, the phosphate group is attached through a phosphoester bond, because phosphate is an acid while glycerol is an alcohol. Therefore, phospholipids are also called as diacyl-glycerophospholipids or simply phosphatidic acid. Now, come to the point, what characteristic of phospholipids is important to their function? To answer this question, let’s look at the structure of the phospholipid. There are two parts in the structure of a phospholipid and these are head and tails.
The phosphate group is considered as a polar head group because of its ability to form H-bonding with water molecules. While two long chain fatty acyl groups are hydrophobic in nature and are considered as hydrophobic tail parts.
Because of this unique property (hydrophobic and hydrophilic moieties within the same molecule), phospholipids are considered as amphiphilic molecules. This is what makes phospholipids one of the most important molecules in the biological system.
Phospholipids form lipid bilayer that constitutes cell membrane and membranes of other cytoplasmic organelles. In lipid bilayer, the polar head group of the phospholipids points outside while the hydrophobic tail parts point inside (avoiding the contact with water molecules).
The polar head group (phosphate group) of the phospholipids can also be modified with some simple organic molecules such as ethanolamine, choline, serine or inositol forming phosphatidylethanolamine, phosphatidylcholine, phosphatidylserine or phosphatidylinositol respectively. These modified glycerophospholipids perform some more advanced functions such as signaling.
I hope you are now clear about what characteristic of phospholipids is important to their function. Lipid bilayer of phospholipids plays an important role in the cellular environment. It separated two different cellular environments forming like a barrier.