a) Lipoproteins are large molecular compounds that are essential to the transport of cholesterol and triglycerides (TGs) within the blood. They contain a lipid core composed of TGs and cholesterol esters surrounded by phospholipids and specialized proteins known as apolipoproteins. The five major families of lipoprotein are chylomicrons, very-low-density lipoproteins (VLDL), intermediate-density lipoproteins (IDL), low-density lipoproteins (LDL), and high-density lipoproteins (HDL).

b) Apolipoproteins are necessary for the structure and enzymatic processes of lipids. Apolipoprotein A1 (apo A1) is a major component of HDL, and apolipoprotein B (apo B) is the main apolipoprotein for the remaining non-HDL lipoproteins.