Lipoproteins

Lipoproteins are biochemical assemblies whose primary role is to transport hydrophobic lipid (fat) molecules in water, as in blood or extracellular fluid. They have a single-layer phospholipid and cholesterol outer shell, with the hydrophilic portions oriented outward toward the surrounding water and lipophilic portions oriented inwards toward the lipid within the particles. Apolipoproteins are embedded in the membrane, both stabilising the complex and giving it functional identity determining its fate. Thus the complex serves to emulsify the fats.

Structure

Lipoproteins are complex particles composed of multiple proteins which, when bound to lipids, form large macromolecular complexes. The proteins incorporated into lipoproteins are called apolipoproteins. They form a shell around the lipids. The outer shell of lipoproteins is composed of phospholipids, which are amphipathic, meaning they have a hydrophilic (water-attracting) head and a hydrophobic (water-repelling) tail.

Function

The primary role of lipoproteins is to transport lipids (fats) around the body in the extracellular fluid, making fats available to body cells for receptor-mediated endocytosis. Lipoproteins are therefore the mode of transport for cholesterol and triglycerides within the body.

Types

There are several types of lipoproteins within the body. The five major types, from least dense, to most dense, are chylomicrons, VLDL, IDL, LDL, and HDL. Each one plays a specific role in the body and has different functions.

Health implications

Abnormal levels or types of lipoproteins, particularly LDL, are strongly implicated in atherosclerosis, which is a major cause of coronary heart disease, stroke, and peripheral vascular disease. Therefore, lipoprotein levels are often measured in medical laboratories as part of a lipid profile.

See also

• Apolipoprotein
• Lipid metabolism
• Lipoprotein(a)
• Lipoprotein lipase
• Lipoprotein-X

Lipoproteins Resources
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