views updated May 14 2018

lipoprotein One of a group of compounds consisting of a lipid combined with a protein. Lipoproteins are the main structural materials of the membranes of cells and cell organelles. They also occur in blood and lymph, being the form in which lipids are transported in these media. Cholesterol is transported in the bloodstream mainly in the form of low-density lipoproteins (LDLs) and is removed by means of LDL receptors in cell membranes; the LDLs are bound to the receptors, which are then taken into the cells. Lack of LDL receptors, occurring as a genetic defect in some individuals, is believed to be a cause of high levels of cholesterol in the blood, predisposing to atherosclerosis. Very low-density lipoproteins (VLDLs) are formed in the liver and are the precursors of LDLs, while high-density lipoproteins (HDLs), the smallest of all lipoproteins, transport cholesterol from tissues to the liver. See also chylomicron.


views updated Jun 11 2018


Lipoproteins are particles in the bloodstream that transport fatty substances called lipids between different organs, glands, and tissues. The interior of the lipoprotein contains triglycerides (glycerol esterified with three fatty acids) and cholesterol esterified with fatty acids. The covering membrane of a lipoprotein contains chemicals more easily soluble in blood than those in the interior, such as free cholesterol, phospholipids (e.g., lecithin), and apoproteins. Since the different lipoproteins contain different amounts of triglycerides and cholesterol, they may be separated by centrifuging them into particles with different densities, including low-density (LDL), high-density (HDL), and very low-density (VLDL) particles. Apoproteins (such as apo A in HDL particles and apo B in VLDL and LDL particles) function to direct the lipoproteins to their destinations or to act as coenzymes to activate certain other enzymes that process the lipoproteins.

Donald A. Smith

(see also: Atherosclerosis; Blood Lipids; Cholesterol Test; HDL Cholesterol; Hyperlipidemia; LDL Cholesterol; Triglycerides; VLDL Cholesterol )


views updated May 11 2018

lipoprotein (lip-oh-proh-teen) n. one of a group of compounds, found in blood plasma and lymph, each consisting of a protein (see apolipoprotein) combined with a lipid (cholesterol, a triglyceride, or a phospholipid). Lipoproteins are important for the transport of lipids in the blood and lymph. high-density l. (HDL) a type of lipoprotein that transports cholesterol from the tissues to the liver. low-density l. (LDL) a type of lipoprotein that is the main form in which cholesterol is transported in the bloodstream, from which it is taken into the cells by binding with LDL receptors. very low-density l. (VLDL) a type of lipoprotein that is the precursor of LDL.


views updated May 29 2018

lipoprotein A water-soluble, conjugated protein in which the prosthetic group is a lipid. Lipoproteins transport lipids in the blood and lymph from the small intestine to the liver and from the liver to fat deposits.


views updated Jun 27 2018

lip·o·pro·tein / ˌlipəˈprōˌtēn; ˌlī-/ • n. Biochem. any of a group of soluble proteins that combine with and transport fat or other lipids in the blood plasma.


views updated Jun 11 2018

lipoprotein A water-soluble, conjugated protein in which the prosthetic group is a lipid.


views updated May 23 2018

lipoproteins Complexes of protein and lipids; see lipids, plasma.