b) Briefly discuss the metabolism of Low Density Lipoproteins (LDL).
ANS- As described in a former post, part of the IDL is not captured by the hepatocyte, but continues in plasma losing TAG and increasing its Cholesterol content, becoming Low Density Lipoproteins or LDL.
The lipid core of LDL is formed mainly by cholesterol esters:
The only apoprotein that is present at the LDL surface is Apo B-100.
Due to the structural changes that occur during the conversion of VLDL to IDL and from IDL to LDL, Apo B expose a domain that can interact with LDL receptors (receptors for Apo B-100) that are located in the liver but also in extrahepatic tissues.
The binding of LDL and the receptor in the hepatocyte surface triggers an endocytosis process ("receptor-mediated-endocytosis"), with the formation of endosomes. Changes in Ph provoke the dissociation between the lipoprotein and the receptor, the receptor returns to the membrane while the endosome fuse with a lysosome; lysosome enzymes hydrolyze the LDL proteins, the cholesterol esters and other lipids.
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