Structure and function:

Triacylglycerols, cholesterol and phospholipids are associatively insoluble in aqueous solution. Therefore, they are transported around the body in the blood as parts of lipoproteins.  These circular micelle-like particles consist of a hydrophobic core of triacylglycerols and cholesterol esters surrounded through an amphipathic coat of protein, cholesterol and phospholipid. The protein elements of lipoproteins are known as apolipoproteins (or apoproteins).  At least 10 variant apoproteins are found in the variant human lipoproteins. Their purpose are to help solubilize the hydrophobic lipids and to act as cellular targeting signals. Lipoproteins are classified into five collections on the basis of their physical and functional properties are described in the table:

-  Chylomicrons are the major and least dense lipoproteins. They transport dietary (exogenous) cholesterol and triacylglycerols   from the intestines to other tissues in the body.

-  Very low density lipoproteins (VLDLs), intermediate density lipoproteins (IDLs) and low density lipoproteins (LDLs) are a group of related lipoproteins that transport internally produced (endogenous) triacylglycerols and cholesterol from the liver to the tissues.

-  High density lipoproteins (HDLs) transport endogenous cholesterol from the tissues to the liver.