Definition: Lipoproteins are complex particles consisting of proteins and fats that circulate in the bloodstream. The chief purpose of lipoproteins is to transport fats -- mainly cholesterol and triglycerides - from place to place through the bloodstream.
Fats are insoluble (they do not dissolve in water) so they have to be "packaged" in such a way that they can flow through the bloodstream. Lipoproteins form a container, made of specialized proteins called apolipoproteins, which enclose the fats, allowing them to be transported to their appropriate destinations.
Examples of Lipoproteins:
Chylomicrons are lipoproteins that deliver triglycerides from the intestines to the liver, muscle, and adipose (fat) tissue. The main apolipoprotein of chylomicrons is APO B-48.
LDL (low density lipoproteins) carry cholesterol from the liver to tissues in the body. The main apolipoprotein of LDL is APO B-100
HDL (high density lipoproteins) carry excess cholesterol from the body's tissues back to the liver. The main apolipoprotein of HDL is APO-A.