ABSTRACT
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vitamins (such as A, D, E, and K), monoglycerides, diglycerides, triglycerides, phospholipids, and others. Lipids are fat-soluble, hydrophobic molecules. They will not, therefore, readily dissolve into the blood plasma. For this reason a class of phospholipoproteins exist to act as carriers of the various lipids in the blood. A phospholipoprotein is a ball of phospholipids packed together to form a monolayer (hydrophilic phosphate end out, hydrophobic lipid end in). The ball structure is maintained by one or more protein structures (various proteins are synthesized that ultimately form various different phospholipoproteins), and the ball structure is also maintained by molecular cholesterol. The different phospholipoproteins exist in order to deliver the various lipid cargos to targeted cells with receptors for a specic phospholipoprotein. Phospholipoproteins are usually referred to simply as “lipoproteins.” The classes of lipoproteins are chylomicrons, high-density lipoproteins (HDL), intermediate-density lipoproteins (IDL), low-density lipoproteins (LDL), and very low-density lipoproteins (VLDL). Figure 4.1 shows how various types of lipoproteins carry lipids in the blood.
