Phosphatidylglycerol is a glycerophospholipid

Glycerophospholipid

Glycerophospholipids or phosphoglycerides are glycerol-based phospholipids. They are the main component of biological membranes.-Structures:...

 found in pulmonary surfactant

Pulmonary surfactant

Pulmonary surfactant is a surface-active lipoprotein complex formed by type II alveolar cells. The proteins and lipids that surfactant comprises have both a hydrophilic region and a hydrophobic region...

.

The general structure of phosphatidylglycerol consists of a L-glycerol 3-phosphate backbone ester-bonded to either saturated or unsaturated fatty acids on carbons 1 and 2. The head group substituent glycerol is bonded through a phosphomonoester. It is the precursor of surfactant and its presence in the amniotic fluid of the newborn indicates fetal lung maturity.

Approximately 98% of alveolar wall surface area is due to the presence of type I cells, with type II cells producing pulmonary surfactant covering around 2% of the alveolar walls. Once surfactant is secreted by the type II cells, it must be spread over the remaining type I cellular surface area. Phosphatidylglycerol is thought to be important in spreading of surfactant over the Type I cellular surface area. The major surfactant deficiency in premature infants relates to the lack of phosphatidylglycerol, even though it comprises less than 5% of pulmonary surfactant phospholipids.

Biosynthesis

L-glycerol-3-phosphate is activated by a CTP

Cytidine triphosphate

Cytidine triphosphate is a pyrimidine nucleoside triphosphate.CTP is a substrate in the synthesis of RNA.CTP is a high-energy molecule equal to ATP, but its role in the organism is more specific than that of ATP....

 and pyrophosphate

Pyrophosphate

In chemistry, the anion, the salts, and the esters of pyrophosphoric acid are called pyrophosphates. Any salt or ester containing two phosphate groups is called a diphosphate. As a food additive, diphosphates are known as E450.- Chemistry :...

 is cleaved off resulting in CDP-diglycerol. Glycerol-3-phosphate is attached to CDP-diglycerol and phosphatidylglycerol phosphate is formed, while CMP

Cytidine monophosphate

Cytidine monophosphate, also known as 5'-cytidylic acid or simply cytidylate, and abbreviated CMP, is a nucleotide that is used as a monomer in RNA. It is an ester of phosphoric acid with the nucleoside cytidine...

 is released. The phosphate group is hydrolysed forming phosphatidylglycerol.
Two phosphatidylglycerols form cardiolipin

Cardiolipin

Cardiolipin is an important component of the inner mitochondrial membrane, where it constitutes about 20% of the total lipid composition. The only other place that cardiolipin can be found is in the membranes of most bacteria. The name ‘cardiolipin’ is derived from the fact that it was first...

, the constituent molecule of the mitochondrial inner membrane.