phospholipides

Phospholipides are a class of amphipathic lipids that form the fundamental structural component of cellular membranes. Each molecule typically contains a glycerol backbone esterified to two fatty acid tails and a phosphate-containing head group, yielding a hydrophobic interior and a hydrophilic exterior that interact with water and ions.

The head group varies, producing different phospholipids such as phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol. In mitochondria and bacterial membranes, other variants like cardiolipin and phosphatidylglycerol are common. The fatty acyl chains can be saturated or unsaturated, influencing membrane properties.

In aqueous environments, phospholipides spontaneously assemble into bilayers, forming the basis of cell membranes and vesicles. The bilayer is a dynamic, fluid structure described by the fluid mosaic model. Saturated chains stiffen the membrane, while unsaturated chains and cholesterol modulate fluidity and thickness.

Biosynthesis occurs mainly in the endoplasmic reticulum through pathways that assemble a diacylglycerol phosphate or a corresponding intermediate, followed by attachment of head groups. Phospholipases and acyltransferases remodel phospholipids, providing signaling precursors such as diacylglycerol and phosphatidylinositol phosphates.

Beyond structural roles, phospholipides participate in signaling, membrane trafficking, coagulation, and apoptosis. Externalization of phosphatidylserine marks cells for clearance, while phosphatidylinositol phosphates coordinate intracellular signaling cascades. Phospholipides are ubiquitous in all cellular membranes across life.