Highest lectrophoretic mobility and least lipid content | Crack PGIMER 22 MAY 2016

Which of the following has highest lectrophoretic mobility and least lipid content:

A. Chylomicrons 
B. HDL 
C. LDL 
D. VLDL
E. IDL

The Answer is. (B) ]HDL :

•.HDL contains lowest amount of triglycerides. It has highest density and highest amount of electrophoretic mobility. In decreasing order of rate of mobility, lipoproteins arranged as :

HDL (Lipoprotein) >VLDL (Pre-3 Lipoprotein) >LDL ( Lipoprotein) >Chylornicron

ü  The basic lipoprotein structure comprises a hydrophobic core of triglycerides and cholesterol esters surrounded by a coat containing polar phospholipids, free cholesterol and apoproteins. Apoproteins ensure indentification of receptors for the exchange and deposition of transported lipid fractions.

ü  First of all chylomicrons, containing dietary triglyceride and a small amount of cholesterol, pass into the circulation via lymphatics. Triglyceride is removed in the peripheral circulation by the endothelial enzyme lipoprotein lipase (LPL). The resulting chylomicron remnant, containing most of the origional cholesterol, is taken up by the liver.

ü  Very-low-density lipoproteins (VLDL) are secreted by the liver and contain endogenously synthesized triglycerides and cholesterol a.o. Triglycerides are progressively removed from VLDL by lipoprotein lipase to produce intermediate density lipoproteins (IDL), which can either be reabsorbed by the liver or further dPPCeted of triglycerides to produce low-density lipoproteins (LDL).

ü  LDL, the major carrier of the plasma cholesterol, are taken up by the liver and peripheral cells, largely via receptor recognizing apoproteins B and E. The cytoplasmic pool of cholesterol is derived partly from LDL and partly by endogenous synthesis from acetyl coenzyme A. In the liver, bile salts are synthesized from this pool and, after secretion in the bile, are partly reabsorbed via the terminal ileum and recirculated.

ü  High-Density lipoproteins (HDL) comprise a heterogeneous fraction of particles which carry 20-30% of the total plasma cholesterol. Precursors of HDL (HDL3) are secreted by the liver and accept cholesterol from cell membranes which is esterified by the enzyme lecithin:cholesterol acyltransferase (LCAT).

ü  HDL are involved in reverse cholesterol transport through their ability to accept free cholesterol, esterify it and transfer the cholesterol to other lipoproteins, but mainly and ultimately to the liver for elimination.