VPB 112: General Veterinary Biochemistry (1+1)

PHOSPHOLIPIDS

• They are so named because; they contain phosphorus in the form of phosphoric acid. In addition, they also contain glycerol, fatty acids and a nitrogenous base.
• Phospholipids contain fatty acids esterified to position 1 and 2 of glycerol and a phosphoryl group at position 3. If only a phosphate group is attached to position 3, then the compound is known as “Phosphatidic acid’ which has no head alcohol. It is an intermediate in the synthesis of triacylglycerols and phospholipids.

• Phospholipids differ from triacylglycerol in possessing one or more highly polar head groups in addition to their non-polar hydrocarbon tail. For this reasons they are often called “polar lipids”. Due to the attachment of polar and non-polar groups in the same structure they are also known as amphipathic lipids.
• Fatty acids found in phosphoglycerides (or glycerophospholipids) have 16 or 18 C atoms.
• Usually one of the fatty acids is saturated and the other is unsaturated.
• The unsaturated fatty acid is always attached to the 2^nd hydroxyl group of the glycerol.
• Different types of phosphoglycerides are named according to the alcohol attached on their polar head group of phosphatidic acid; all of these phosphoglycerides except sphingomyelins may be regarded as derivative of phosphatidic acid.
• There are two classes of phospholipids, viz. those that have glycerol as the back bone and those that contain sphingosine as back bone.
• The phospholipids containing glycerol as the back bone:
• Phophatidic acid and phosphatidyl glycerol
• Phosphatidylcholine
• Phosphatidylethanolamine
• Phosphatidylinositol
• Phosphatidylserine
• Lysophospholipids
• Plasmalogens
• Cardiolipins.
• The phospholipids containing sphingosine as the back bone
• Sphingomyelins.