LDL is a type of cholesterol that transports cholesterol from the liver to tissues throughout the body. It contains the protein apolipoprotein B-100. LDL particles enter cells through receptor-mediated endocytosis. The LDL receptors on cells recognize and bind to apolipoprotein B-100, triggering the LDL particle to be engulfed by the cell. Inside the cell, the LDL particle is degraded to release free cholesterol. High intracellular cholesterol levels inhibit cholesterol synthesis and reduce production of LDL receptors to maintain cholesterol homeostasis within the cell.

1. Low Density Of Lipoprotein
Presented by: Peshawa Ibrahim

2. LDL low density of lipoprotine
 LDL is a bad cholesterol, it transport cholesterol from liver to peripheral tissues,
the transported cholesterol has follow fats for syntheses of steroid LDL contain
only one lipoprotein Apo B-100 (Apolipoprotein B100 (apoB100) is a protein that
plays a role in moving cholesterol around your body. It is a form of low density
lipoprotein (LDL).

4. Metabolism of LDL
 LDL particles contain much less triacylglycerol than their VLDL predecessors, and
have a high concentration of cholesterol and cholesteryl esters.
 Receptor-mediated endocytosis:
 1) The primary function of LDL particles is to provide cholesterol to the
peripheral tissues (or return it to the liver). They do so by binding to cell surface
mem-brane LDL receptors that recognize Apo B-100 (but not Apo B-48). Because
these LDL receptors can also bind Apo E, they are known as Apo B-100/ Apo E
receptors. A similar mechanism of receptor-mediated endocytosis is used for the
cellular uptake and degradation of chylomicron remnants and IDLs by the liver.

5.  2) LDL receptors are negatively charged glycoproteins that are clustered in pits
on cell membranes. The cytosolic side of the pit is coated with the protein
clathrin, which stabilizes the shape of the pit.
 3) After binding, the LDL-receptor complex is internalized by endocytosis.

6.  4) The vesicle containing LDL loses its clathrin coat and fuses with other
similar vesicles, forming larger vesicles called endosomes.
 5) The pH of the endosome falls (due to the proton-pumping activity of
endosomal ATPase), which allows separation of the LDL from its receptor. The
receptors then migrate to one side of the endosome, whereas the LDLs stay
free within the lumen of the vesicle.
 The receptors can be recycled, whereas the lipoprotein remnants in the
vesicle are transferred to lysosomes and degraded by Lysol - somal acid
hydrolases, releasing free cholesterol, amino acids, fatty acids, and
phospholipids. These compounds can be reutilized by the cell.

8. Effect of endocytosed cholesterol on
cellular cholesterol home-stasis:
 The chylomicron remnant-, IDL-, and LDL-derived cholesterol affects cellular
cholesterol content in several ways. First, HMG CoA(3-hydroxy-3-methyl-glutaryl-
coenzyme A reductase) reductase is inhibited by high cholesterol, as a result of
which, de novo cholesterol synthesis decreases. Second, synthesis of new LDL
receptor protein is reduced by decreasing the expression of the LDL receptor
gene, thus limiting further entry of LDL cholesterol into cells. Third., if the
cholesterol is not required immediately for some structural or synthetic purpose,
it is esterified transfers a fatty acid from a fatty acyl CoA derivative to cholesterol,
producing a cholesteryl ester that can be stored in the cell.

9. Thanks for your attention
Peshawa mangury