Glycerolipids

Glycerolipids are a broad class of lipids built on a glycerol backbone and characterized by fatty acids esterified to the glycerol at one, two, or three positions. They include mono-, di-, and triacylglycerols (MAG, DAG, and TAG) as well as glycerophospholipids, in which a phosphate-containing head group is attached to the glycerol backbone. The common feature is the glycerol core with fatty acyl chains linked by ester bonds.

The major glycerolipids are MAGs, DAGs, and TAGs. TAGs are the predominant form of dietary and stored fat in animals, serving as long‑term energy reserves in adipose tissue. Glycerophospholipids, such as phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol, are essential components of cellular membranes. Cardiolipin is a distinctive dimeric phospholipid found mainly in mitochondrial membranes.

Functions of glycerolipids are diverse. TAGs store energy and insulate tissues. Glycerophospholipids form the structural basis of cellular membranes and create membrane curvature and compartments. Some glycerolipid intermediates act as signaling molecules: diacylglycerol (DAG) functions as a second messenger activating protein kinase C, while certain phospholipids participate in signaling pathways through phosphorylated derivatives. Monoacylglycerols and related lipids also participate in cellular signaling and metabolism.

Biosynthesis occurs in the endoplasmic reticulum and involves distinct pathways. TAG synthesis proceeds via the glycerol-3-phosphate pathway with enzymes such as GPAT, AGPAT, and DGAT. Phospholipid synthesis often follows the Kennedy pathway, which builds phosphatidylcholine and phosphatidylethanolamine from head groups like choline or ethanolamine. Lipid remodeling and turnover are mediated by various lipases and acyltransferases.

Glycerolipids are ubiquitous in plants, animals, and microbes, with dietary, metabolic, and signaling roles. Dysregulation of glycerolipid metabolism is linked to metabolic diseases and obesity.