[Fatty acids--1. occurrence and biological significance].

Fatty acids are monocarboxylic acids with chain-length 2-36 carbon atoms and 0-6 double bonds. Their physico-chemical properties are reflected also in the compounds, where fatty acids represent an important component (phospholipids, triglycerides), as well as in higher organized structures (plasma membranes, lipoproteins). Fatty acids are synthesized from two-carbon precursors; their degradation by beta-oxidation is accompanied by energy-release. Fatty acids are classified with respect to double bonds into saturated, monounsaturated and polyunsaturated. Simple lipids are esters of fatty acids and organic alcohols - cholesterol, glycerol and sphingosine and their derivatives. Endogenous acids can be desaturated up to Delta9 position; desaturation to other position is possible only from exogenous (essential) acids [(linoleic (n-6 series) and alpha-linolenic (n-3 series)]. Circulating lipids (in form of lipoproteins) consist of cholesterol esters and triglycerides in nonpolar core and phosphatidylcholin and sphingomyelin in the polar envelope of lipoproteins. Nonesterified fatty acids (product of lipolysis and source for lipid synthesis) are bound to plasma albumin. Membrane lipids, which ensure membrane fluidity and other functions, consist of phosphatidylcholine, phosphatidylethanolamine, sphingomyelin and some other (minor) phospholipids.