LEARNING OBJECTIVES
In this article, author has explained the different types of glycerophospholipids.
The phospholipids which contain glycerol as alcohol is called glycerophospholipids.
In glycerophospholipid, C1 and C2 are esterified with the fatty acids while C3 has a phosphate group. They are major phospholipids that occur in the cell membrane. Phosphatidic acid is involved in the formation of glycerophospholipid. The phosphate group of phosphatidic acid is esterified with the hydroxyl group of nitrogen base or another group.
Phosphatidic acid
Table of Contents
Phosphatidic acid is the most common phospholipid. Phosphatidic acid does not occur in the tissues. It is the intermediate in the formation of triacylglycerols and phospholipids. It is involved in the formation of glycerophospholipid. The phosphate group of phosphatidic acid is esterified with the hydroxyl group of nitrogen base or another group.
The other glycerophospholipids are considered derivatives of phosphatidic acid.
Lecithins
Lecithin is also known as phosphatidylcholine. Lecithins are the most abundant phospholipids occurring in the cell membrane. Lecithins are derived from phosphatidic acid. The choline acts as a base in it. Lecithins store choline in the body. They have both structural and metabolic functions.
Lecithins are of two types:
1. Dipalmitoyl lecithin
Dipalmitoyl lecithin is very important phosphatidylcholine found in the lungs. They act as lung surfactants and are very important for the normal functioning of the lungs. Dipalmitoyl lecithin prevents alveolar collapse. It prevents the adherence of the inner surface of the lungs due to surface tension. Due to the absence of dipalmitoyl lecithin, respiratory distress syndrome can occur in infants.
2. Lysophospholipids
When two fatty acids are removed from the glycerophospholipid, lysophospholipids are produced. Fatty acids are removed from C1 or C2. They are also known as lysolecithins. Lysophosphatidylcholine and lysophosphatidylethanolamine are called examples of lysophospholipids.
Cephalins
Cephalins are also known as phosphatidylethanolamine. The base in phosphatidylethanolamine is ethanolamine. Thus cephalins and lecithins differ with respect to the base. Thrmoboplastin is a cephaline. Thromboplastin is needed to start the process of clotting.
Phosphatidylinositol
Phosphatidylinositol is a major component of the cell membrane. When the stereoisomer Myo-inositol is attached to phosphatidic acid, it produces phosphatidylinositol. Phosphatidylinositol mediates the signal of various hormones like oxytocin and vasopressin.
Phosphatidylserine
This glycerophospholipid contains amino acid serine. It is found in most tissues. Phosphatidylthreonine is also found in certain issues.
Plasmalogens
In plasmalogens, the fatty acid is attached to carbon 1 of the glycerol by the ether linkage instead of the ester linkage. The fatty acid present at C1 is unsaturated.
Plasmalogens consist of three classes:
- Phosphatidylcholine
- Phosphatidylserine
- Phosphatidylethanolamine
Plasmalogen is a factor that activates the platelets. They activate platelet aggregation and degranulation. Plasmalogen is also found in cardiac muscles and myelin.
Cardiolipin
This glycerophospholipid is isolated from the cardiac muscles. Therefore, it is named cardiolipin. Cardiolipin consists of two phosphatidic acids held by additional glycerol molecules through the phosphate group. Cardiolipin is very essential for the functioning of mitochondria. It is a critical component of the inner mitochondria membrane. it helps in the electron transport system. A decrease in cardiolipin concentration can cause a problem with the function of mitochondria. It can also cause other problems like aging, hypothyroidism, and cardio skeletal myopathy. Cardiolipin is the only human glycerophospholipid that has antigenic properties.