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lipoprotein |
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lipoprotein (lĭp'əprō`tēn), any organic compound that is composed of both protein protein, any of the group of highly complex organic compounds found in all living cells and comprising the most abundant class of all biological molecules. Protein comprises approximately 50% of cellular dry weight. ..... Click the link for more information. and the various fatty substances classed as lipids lipids, a broad class of organic products found in living systems. Most are insoluble in water but soluble in nonpolar solvents. The definition excludes the mineral oils and other petroleum products obtained from fossil material. ..... Click the link for more information. , including fatty acids fatty acid, any of the organic carboxylic acids present in fats and oils as esters of glycerol . Molecular weights of fatty acids vary over a wide range. The carbon skeleton of any fatty acid is unbranched. Some fatty acids are saturated, i.e. ..... Click the link for more information. and steroids steroids, class of lipids having a particular molecular ring structure called the cyclopentanoperhydro-phenanthrene ring system. Steroids differ from one another in the structure of various side chains and additional rings. ..... Click the link for more information. such as cholesterol cholesterol (kəlĕs`tərōl') ..... Click the link for more information. . The lipoprotein complex of proteins and steroids is usually provided by a weak, noncovalent interaction; proteins complexed with some other lipids do so by the information of covalent chemical bonds. There are several types of lipoproteins present in human blood, including low-density lipoproteins (LDLs)—molecules with a larger molecular weight and a relatively low percentage of protein—and high-density lipoproteins (HDLs)—molecules with a smaller molecular weight and a relatively high percentage of protein. LDLs are the main transport for cholesterol through the body. HDLs appear to carry excess cholesterol to the liver for processing. Studies have found that high levels of HDLs, which seem to retard or even reverse the formation of cholesterol plaque in the arteries (see arteriosclerosis arteriosclerosis (ärtĭr'ēōsklərō`sis) ..... Click the link for more information. ), reduce the risk of cardiovascular disease. Cell membranes are essentially lipoprotein in nature; the membrane is a continuous sheet of lipid molecules, largely phospholipids phospholipid (fŏs'fōlĭp`ĭd) ..... Click the link for more information. , in close association with proteins that either face one side of the membrane or penetrate all the way through the membrane. lipoproteinAny of a class of organic compounds that contain both lipid (fat) and protein. They may be soluble (those in egg yolk and blood plasma) or insoluble (those in cell membranes) in water and water solutions. Lipoproteins in blood plasma are the mode of transport for cholesterol, insoluble by itself. Low-density lipoproteins (LDLs) carry cholesterol from the liver, where it is made, to the cells, where it is used; high-density lipoproteins (HDLs) may carry excess cholesterol back to the liver for breakdown and excretion. LDL-bound cholesterol is primarily responsible for deposits in arteries (see arteriosclerosis) that can lead to coronary heart disease, angina pectoris, myocardial infarction, or stroke. HDL does not form such deposits and may actually retard or reduce their buildup. |
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