Lipoproteins Research Paper

1.4. Lipoproteins

Lipoprotein is a biochemical molecule that composed of both proteins and lipids, and through which fats move through the bloodstream. Lipoproteins, act as transport vehicles for triacylglycerol and cholesterol in the plasma as lipids are hydrophobic macromolecules that are insoluble in water [117].

1.4.1. Lipoproteins Structure

Lipids, such as cholesterol, triacylglycerols, and phospholipids, are not soluble in aqueous solution. Therefore, they are transported in the blood as lipoproteins, globular micelle like particles that have a nonpolar core of triacylglycerols and cholesteryl esters and an amphipathic coating of protein, phospholipid, and cholesterol (reference). the positive charge of the nitrogen atom of the phospholipid

Lipoproteins Classification Lipoproteins can be differentiated depending upon:

1- The basis of their density.

2- The type of apolipoproteins they have.

Table (1-2): lipoproteins classification according to density (reference).

The percentage and the type of lipid compounds in the lipoprotein affect its density (the lower the density of a lipoprotein, the more the lipid it contains relative to protein). The four major types of lipoproteins are chylomicrons, very low-density lipoprotein (VLDL), low-density lipoprotein (LDL), and high-density lipoprotein (HDL). (intermediate density lipoproteins IDL, which are intermediate between VLDL and LDL (reference).

1.4.2.1. Chylomicrons

Chylomicrons act to transport exogenous triacylglycerols and cholesterol dietary lipids from the intestines to the tissues. Chylomicrons are the largest size and lowest density lipoproteins and and contain the uppermost percentage of lipid and the lowest percentage of protein (figure1-14). In the bloodstream, chylomicrons acquire apoC-II and apoE from plasma HDLs [120]. The major sites for removal of chylomicrons are the muscle and liver. where they are metabolized further [120] as shown in. figure(1-15) Figure (1-14 ) chylomicron structure

LDL is formed from VLDL and some are released by the liver. LDL is a major transport form of cholesterol and cholesteryl esters in the circulation.. LDL has a specific cell surface receptors [123] as show in figure (1-10). The amount of LDL receptor is regulated by the cellular requirement for lipids, with the primary regulatory lipid being cholesterol [124]. High level of LDL-C is connected with elevated risk of heart disease. LDL-C is the “bad cholesterol” of the common