lipidi

Lipids are a broad class of organic compounds characterized by their hydrophobic or amphipathic nature and their general insolubility in water. Major lipid classes include fatty acids, triglycerides, glycerophospholipids (phospholipids), sphingolipids, and sterols. They are distinct from carbohydrates, proteins, and nucleic acids as macronutrients with diverse structures and roles in biology.

Fatty acids are long hydrocarbon chains with a terminal carboxyl group. They can be saturated or unsaturated, and double bonds may be in cis or trans configurations. Triglycerides consist of three fatty acids esterified to glycerol and primarily serve as energy storage in adipose tissue. Glycerophospholipids and sphingolipids are key components of cellular membranes, while cholesterol and other sterols modulate membrane properties and serve as precursors for steroid hormones and bile acids.

Biological roles of lipids include membrane structure and permeability, signaling, and energy storage. Lipids also participate in the formation of lipid droplets, lipid rafts, and various signaling molecules such as eicosanoids and steroid hormones. Lipid metabolism integrates digestion, absorption, transport, and synthesis. Dietary fats are emulsified by bile salts, hydrolyzed by pancreatic lipase, absorbed as fatty acids and monoacylglycerols, re-esterified, and packaged into lipoproteins for transport. In cells, fatty acids undergo beta-oxidation in mitochondria to generate acetyl-CoA for energy production, while fatty acids and cholesterol can be synthesized de novo.

Health and nutrition considerations include the management of lipid levels to reduce disease risk. Common clinical measures are total cholesterol, low-density lipoprotein (LDL), high-density lipoprotein (HDL), and triglycerides. Diets emphasizing unsaturated fats over saturated and trans fats influence lipid profiles and health outcomes. Essential fatty acids must be obtained from the diet.