lipider

Lipider are a diverse class of organic molecules that are predominantly hydrophobic and poorly soluble in water. They encompass fats, oils, waxes, sterols and related compounds. Lipider provide energy, form the structural basis of cellular membranes, and participate in signaling and regulation. They may be synthesized by organisms or supplied by the diet, and are studied in biochemistry and nutrition.

Lipider are commonly classified into simple lipider (triglycerides, fatty acids, waxes), compound lipider (phospholipids, glycosphingolipids, lipoproteins), and derived lipider (steroids, terpenoids). Within membranes, phospholipids and cholesterol establish bilayers with embedded proteins, whereas lipoproteins transport lipider in blood and lymph. Some vitamins (A, D, E, K) are fat-soluble and rely on lipider for absorption.

Fatty acids vary in chain length and saturation. Saturated fatty acids have no double bonds, while unsaturated fatty acids contain cis double bonds that introduce kinks, reducing packing density. Lipider such as triglycerides store energy efficiently (about 9 kcal per gram) and serve as insulation and padding in organisms.

Digestion and metabolism involve emulsification by bile acids, hydrolysis by pancreatic lipase, and absorption as fatty acids and monoglycerides. In cells, re-esterification forms triglycerides for storage in adipocytes or assembly into lipoprotein particles (chylomicrons, VLDL, LDL, HDL) for transport. Beta-oxidation of fatty acids in mitochondria yields acetyl-CoA for energy production.