LDL Metabolism
Low-density lipoprotein (LDL) originates in the liver and is transported around an animal by the blood stream. From there it is taken up by other cells, such as fibroblasts, and degraded: this provides a source of cholesterol for the growth of these other cells. LDL in the blood binds to LDL receptors on the surface of fibroblasts; these receptors concentrate in coated pits (they are about 200x as concentrated here as along the rest of the cell’s plasma membrane) and are internalised when the pit becomes a coated vesicle. The itinerary of the LDL receptor inside the cell is complex, but it spends little time there. Within a fraction of a minute, it has released its LDL cargo and is returned to the cell surface by exocytosis. It is now ready for another round of LDL clearance.
High levels of LDL in the blood are observed in atherosclerosis and associated with the disease; the endocytic cycle reduces LDL through consuming it. This may or may not be useful in regulating increased levels of LDL, although it may have limitations, or not increase at all in the presence of extra LDL molecules.
Read more about this topic: Endocytic Cycle
Famous quotes containing the word metabolism:
“He’s got a fifteen percent metabolism with an overactive thyroid and a glandular affectation of about three percent. With a one percent mentality. He’s what we designate as the Crummy Moronic type.”
—Robert Pirosh, U.S. screenwriter, George Seaton, George Oppenheimer, and Sam Wood. Dr. Hugo Z. Hackenbush (Groucho Marx)