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[Biochemistry](https://durgical.com/en/biochemistry/) · Topic

# Phospholipids

Phospholipids have a phosphate head that attracts water and two fatty tails that avoid it, so they form the bilayers of every membrane.

Updated 2026-11-01

## Key facts

- Glycerophospholipid: glycerol + two fatty acids (C1 and C2) + a phosphate on C3 linked to a head group (choline, ethanolamine, serine, inositol).
- Phosphatidic acid is the common precursor of glycerophospholipids and triacylglycerol.
- Phosphatidylcholine (lecithin) is the most abundant membrane lipid; dipalmitoyl phosphatidylcholine is the main component of lung surfactant.
- Asymmetry: phosphatidylcholine and sphingomyelin dominate the outer leaflet; phosphatidylserine and phosphatidylethanolamine the inner one.
- Phospholipase A₂ frees arachidonic acid from C2 (eicosanoids); phospholipase C splits PIP₂ into IP₃ and DAG (second messengers).

## In detail

- 1. Synthesis: glycerol 3-phosphate + 2 acyl-CoA → phosphatidic acid in the smooth endoplasmic reticulum.
- 2. Kennedy pathway: choline or ethanolamine is activated with CDP and joined to diacylglycerol.
- 3. Phosphatidylinositol and cardiolipin come from CDP-diacylglycerol; cardiolipin is typical of the inner mitochondrial membrane.
- 4. Plasmalogens (ether bond at C1) are rich in myelin and heart; their synthesis starts in the peroxisome.
- 5. Phospholipases A₁, A₂, C and D cut different bonds; each has a role in signalling or digestion.

**Also called**
Glycerophospholipids

## Clinical notes

- Preterm newborns have little surfactant, so alveoli collapse (respiratory distress syndrome). The amniotic fluid lecithin/sphingomyelin ratio estimates lung maturity.
- Phosphatidylserine exposed on the outer leaflet is the apoptosis signal that macrophages recognise.
- Some snake venoms contain phospholipase A₂, which lyses red cell membranes.

## Related conditions

- [Acute respiratory distress syndrome (ARDS)](https://durgical.com/en/conditions/acute-respiratory-distress-syndrome/)

## Related

- [Phosphatidylcholine (lecithin)](https://durgical.com/en/biochemistry/molecules/phosphatidylcholine/)
- [Sphingomyelin](https://durgical.com/en/biochemistry/molecules/sphingomyelin/)
- [Lipid chemistry](https://durgical.com/en/biochemistry/topics/lipid-chemistry/)
- [Membrane structure](https://durgical.com/en/biochemistry/topics/membrane-structure/)
- [Eicosanoids: prostaglandins, thromboxanes and leukotrienes](https://durgical.com/en/biochemistry/topics/eicosanoids-prostaglandins-thromboxanes-and-leukotrienes/)

## Test yourself

Think of the answer, then tap the question to see it.

## Which phospholipid is the main component of lung surfactant?

Dipalmitoyl phosphatidylcholine (a lecithin), which lowers alveolar surface tension.

## Which molecule is the common precursor of phospholipids and triacylglycerol?

Phosphatidic acid (diacylglycerol with a phosphate on C3).

## Which enzyme frees arachidonic acid from the membrane?

Phospholipase A₂, which cuts the fatty acid off carbon 2 of glycerol.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Glycerophospholipid biosynthesis](https://reactome.org/PathwayBrowser/#/R-HSA-1483206) (Reactome, 2026); [Synthesis of PC](https://reactome.org/PathwayBrowser/#/R-HSA-1483191) (Reactome, 2026); [Phospholipid metabolism](https://reactome.org/PathwayBrowser/#/R-HSA-1483257) (Reactome, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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