Lipoproteins are usually classified by their densities.
The density increases as the protein content increases. Recall that the protein content mainly refers to the proteins embedded in the plasma membrane, the apolipoproteins. This is what allows the lipoprotein to be soluble in the water content of the blood.
There are five major types, each of which has a different function.
Types of Lipoproteins
Chylomicrons: Very large particles that carry dietary lipids; they are associated with a variety of apolipoproteins (A-C, E). This is the very first type produced in the body shortly after triglycerides have been catalytically degraded into two fatty acids and a monoglyceride by pancreatic lipases within the small intestines and absorbed in the cells lining the walls of the small intestines. Chylomicrons are then produced within the enterocytes (the intestinal absorptive cells) and released into the lymph duct prior to being released in the blood stream via the thoracic duct.
Very-Low Density Lipoprotein (VLDL): Low density particles that carry endogenous triglycerides and to a less extent cholesterol from the liver to other parts of the body (the periphery).
Intermediate Density Lipoprotein (IDL): Carries cholesterol esters (the hydroxyl group of the cholesterol is esterified to an unsaturated fatty acid) and triglycerides.
Low Density Lipoprotein (LDL): Carries cholesterol esters from the liver to rest of the body and is associated with apolipoprotein B100. Often referred to as the “Bad” cholesterol.
High Density Lipoprotein (HDL): Carries cholesterol esters from organs back to the liver for degradation into bile acids such as taurocholate and glycocholate. Often referred to as the “Good” cholesterol.
