Lipids constitute a heterogeneous class of water-insoluble organic molecules defined by solubility in non-polar solvents and specific elemental composition including carbon, hydrogen, oxygen, phosphorus, nitrogen, or sulfur. Unlike carbohydrates or proteins where chemical structure dictates function, lipid theory emphasizes physical properties such as hydrophobicity to classify functional diversity within biochemistry. The core theoretical framework establishes that this insolubility drives their physiological roles in energy storage via high caloric oxidation yield and the formation of structural barriers for cellular insulation and signaling.
Lipids are classified functionally into structural, signaling, and storage classes, and their biological behavior follows from the amphipathic principle: a molecule bearing both a hydrophilic polar r…