Glycerophospholipid
[3] The term glycerophospholipid signifies any derivative of glycerophosphoric acid that contains at least one O-acyl, or O-alkyl, or O-alk-1'-enyl residue attached to the glycerol moiety.
They are usually organized into a bilayer in membranes with the polar hydrophilic heads sticking outwards to the aqueous environment and the non-polar hydrophobic tails pointing inwards.
[8] When the letters "sn" appear in the nomenclature, by convention the hydroxyl group of the second carbon of glycerol (2-sn) is on the left on a Fischer projection.
There is a negative charge on the phosphate and, in the case of choline or serine, a positive quaternary ammonium ion.
The phosphate ester portion ("head") is hydrophilic, whereas the remainder of the molecule, the fatty acid "tail", is hydrophobic.
An egg yolk has a high concentration of lecithins, which are commercially important as an emulsifying agent in products such as mayonnaise.
Phosphatidylinositol makes up a small component of the cytosol in eukaryotic cell membranes and gives molecules a negative charge.
The glycolipids include phosphatidyl sugars where the alcohol functional group is part of a carbohydrate.
The cell membrane seen under the electron microscope consists of two identifiable layers, or "leaflets", each of which is made up of an ordered row of glycerophospholipid molecules.
Each glycerophospholipid molecule consists of a small polar head group and two long hydrophobic chains.
[13] Their roles as storage centers for secondary messengers in the membrane is also a contributing factor to their ability to act as transporters.
For example, they are important constituents of lipoproteins (soluble proteins that transport fat in the blood) hence affect their metabolism and function.
The main function of these classes of glycerophospholipids in the neural membranes is to provide stability, permeability and fluidity through specific alterations in their compositions.
The length of glycerophospholipid acyl chain and the degree of saturation are important determinants of many membrane characteristics including the formation of lateral domains that are rich in polyunsaturated fatty acids.
Receptor-mediated degradation of glycerophospholipids by phospholipases A(l), A(2), C, and D results in generation of second messengers, such as prostaglandins, eicosanoids, platelet activating factor and diacylglycerol.
Marked alterations in neural membrane glycerophospholipid composition have been reported to occur in neurological disorders.
These processes along with the accumulation of lipid peroxides and compromised energy metabolism may be responsible for the neurodegeneration observed in neurological disorders.
PA can be dephosphorylated leading to the formation of diacylglycerol which is essential in the synthesis of phosphatidylcholine (PC).
In a pathway called the Kennedy pathway, the polar heads are added to complete the formation of the entire structure consisting of the polar head regions, the two fatty acid chains and the phosphate group attached to the glycerol backbone.
In this Kennedy pathway, Choline is converted to CDP-Choline which drives the transfer of the polar head groups to complete the formation of PC.
