Phospholipide

Phospholipide (phospholipid in English) is a class of lipids that form a major component of cell membranes. They are amphipathic molecules with a glycerol backbone attached to two fatty acid chains and a phosphate-containing head group. The fatty acid tails are hydrophobic, while the head group is hydrophilic, enabling phospholipids to assemble into bilayers with a hydrophobic interior and hydrophilic surfaces.

Most are glycerophospholipids, and common head groups include choline, ethanolamine, serine, and inositol. Examples are phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol, and cardiolipin. The head group determines the lipid’s charge and interactions; for example, phosphatidylserine carries a negative charge at physiological pH, whereas phosphatidylcholine is zwitterionic.

In membranes, phospholipids provide structure and barriers, influence fluidity and curvature, and participate in microdomain formation. They also serve as reservoirs for signaling molecules: phospholipase C cleavage of phosphatidylinositol-4,5-bisphosphate yields DAG and IP3; phospholipases can release fatty acids such as arachidonic acid from fatty acyl chains.

Biosynthesis occurs mainly in the endoplasmic reticulum, with remodeling of fatty acid chains by specific acyltransferases to produce tissue-specific species. Cardiolipin is synthesized in mitochondria and is enriched in certain membranes. Phospholipid composition can be remodeled in response to temperature, diet, and cellular state.

Alterations in phospholipid composition and exposure of certain head groups, such as phosphatidylserine on the outer leaflet, have functional and clinical implications, including roles in apoptosis and inflammation. Diet contributes to cellular phospholipid pools through intake of glycerophospholipids and their precursors.