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Chylomicrons, intermediate- density- lipoproteins (IDLs), low- density- lipoproteins (LDLs), and very low-density lipoproteins (VLDLs) are all serum lipoproteins. What is the correct ordering of these particles from the lowest to the highest density?

A. LDLs, IDLs, VLDLs and chylomicrons

B. Chylomicrons, VLDLs, IDLs, LDLs

C.VLDLs, IDLs, LDLs and Chylomicrons

D.LDLs, VLDLs, IDLs, Chylomicrons

E. Chylomicrons, IDLS, VLDLs and LDLs.

The correct answer is B- Chylomicrons, VLDLs, IDLs, and LDLs

Based on density Lipoproteins can be classified as follows

Since fat is less dense than water, the density of a lipoprotein decreases as the proportion of lipid to protein increases.  Lipoproteins with high lipid content will have low density and so float on centrifugation. Those with high protein content sediment easily and have a high density. They are separated by Ultracentrifugation. Depending upon the floatation constant (Sf), Five major groups of lipoproteins have been identified that are important physiologically and in clinical diagnosis. These are

 (i) Chylomicrons, derived from intestinal absorption of triacylglycerol and other lipids; Density is generally less than 0.95 while the mean diameter lies between 100- 500 nm

 (ii) Very low density lipoproteins (VLDL), derived from the liver for the export of triacylglycerol; density lies between 0.95- 1.006 and the mean diameter lies between 30-80 nm.

 (iii) Intermediate density lipoproteins (IDL) are derived from the catabolism of VLDL, with a density ranging intermediate between Very low density and Low density lipoproteins i.e. ranging between 1.006-1.019 and the mean diameter ranges between 25-50 nm.

 (iv)Low-density lipoproteins (LDL), representing a final stage in the catabolism of VLDL; density lies between 1.019-1.063 and mean diameter lies between 18-28 nm

 (iv) High-density lipoproteins (HDL), involved in cholesterol transport and also in VLDL and chylomicron metabolism. Density ranges between 1.063-1.121 and the mean diameter varies between 5-15 nm.

 Classification of lipoproteins

Figure-  The relationship of density and mean diameter of lipoproteins


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