PathwayStep1965 PathwayStep1878 PathwayStep1850 PathwayStep1608 PathwayStep1665 PathwayStep1513 PathwayStep1399 PathwayStep1464 PathwayStep1438 PathwayStep1264 PathwayStep2019 Phospholipid metabolism Fatty acid, triacylglycerol, and ketone body metabolism Metabolism of steroid hormones and vitamins A and D Bile acid and bile salt metabolism Regulation of Cholesterol Biosynthesis by SREBP (SREBF) Cholesterol biosynthesis Peroxisomal lipid metabolism Lipid and lipoprotein metabolism Metabolism of lipids and lipoproteins Authored: Jassal, B, Gillespie, ME, Gopinathrao, G, D'Eustachio, P, 2007-02-02 21:56:36 Edited: D'Eustachio, P, Joshi-Tope, G, 0000-00-00 00:00:00 Lipids are hydrophobic but otherwise chemically diverse molecules that play a wide variety of roles in human biology. They include ketone bodies, fatty acids, triacylglycerols, phospholipids and sphingolipids, eicosanoids, cholesterol, bile salts, steroid hormones, and fat-soluble vitamins. They function as a major source of energy (fatty acids, triacylglycerols, and ketone bodies), are major constituents of cell membranes (cholesterol and phospholipids), play a major role in their own digestion and uptake (bile salts), and participate in numerous signaling and regulatory processes (steroid hormones, eicosanoids, phosphatidylinositols, and sphingolipids). Because of their poor solubility in water, most lipids in extracellular spaces in the human body are found as complexes with specific carrier proteins. Regulation of the formation and movement of these lipoprotein complexes is a critical aspect of human lipid metabolism, and lipoprotein abnormalities are associated with major human disease processes including atherosclerosis and diabetes.<p>The central steroid in human biology is cholesterol, obtained from animal fats consumed in the diet or synthesized de novo from acetyl-coenzyme A. (Vegetable fats contain various sterols but no cholesterol.) Cholesterol is an essential constituent of lipid bilayer membranes and is the starting point for the biosyntheses of bile acids and salts, steroid hormones, and vitamin D. Bile acids and salts are mostly synthesized in the liver. They are released into the intestine and function as detergents to solubilize dietary fats. Steroid hormones are mostly synthesized in the adrenal gland and gonads. They regulate energy metabolism and stress responses (glucocorticoids), salt balance (mineralocorticoids), and sexual development and function (androgens and estrogens). At the same time, chronically elevated cholesterol levels in the body are associated with the formation of atherosclerotic lesions and hence increased risk of heart attacks and strokes. The human body lacks a mechanism for degrading excess cholesterol, although an appreciable amount is lost daily in the form of bile salts and acids that escape recycling.<p>Aspects of lipid metabolism currently annotated in Reactome include lipid digestion, mobilization, and transport; fatty acid, triacylglycerol, and ketone body metabolism; peroxisomal lipid metabolism; phospholipid and sphingolipid metabolism; cholesterol biosynthesis; bile acid and bile salt metabolism; and steroid hormone biosynthesis. Reactome Database ID Release 43556833 Reactome, http://www.reactome.org ReactomeREACT_22258 Sphingolipid metabolism Arachidonic acid metabolism alpha-linolenic (omega3) and linoleic (omega6) acid metabolism