Lipide

Lipide refers to a broad and diverse group of organic compounds that are predominantly hydrophobic or amphiphilic. They are largely insoluble in water and soluble in nonpolar solvents such as chloroform or ether. The class includes fatty acids, glycerides (triglycerides and diglycerides), phospholipids, sphingolipids, sterols and waxes, among others. Lipides play essential structural and functional roles in biology and vary widely in chemical composition and properties.

Classification of lipides encompasses several major groups. Fatty acids are long hydrocarbon chains with a terminal carboxyl group and can be saturated or unsaturated. Glycerolipids, such as triglycerides (fats and oils), primarily store energy, while diglycerides and monoglycerides are intermediate forms. Phospholipids and sphingolipids are major components of cellular membranes; they are amphipathic, with hydrophilic heads and hydrophobic tails that organize into bilayers. Sterols, including cholesterol, regulate membrane fluidity and serve as precursors to steroid hormones and bile acids. Additional lipids like waxes provide protective coatings.

Functions of lipides are diverse. They supply a concentrated source of energy and provide insulation and protection for organs. In membranes, they form bilayers and influence fluidity and permeability; cholesterol modulates membrane properties. Lipids participate in signaling through steroid hormones, eicosanoids, and fat-soluble vitamins (A, D, E, K). They are transported in the bloodstream within lipoproteins.

Digestion and metabolism involve emulsification by bile salts, hydrolysis by pancreatic lipase, and absorption of fatty acids and monoglycerides as micelles. These are reassembled into triglycerides and packaged into chylomicrons for transport; stored lipids in adipose tissue can be mobilized for energy when needed.