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).

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.

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.

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.

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

Sources: Glycerophospholipid biosynthesis (Reactome, 2026); Synthesis of PC (Reactome, 2026); Phospholipid metabolism (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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Representative model, for educational purposes only.