Receptor Mediated Endocytosis

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Receptor-mediated endocytosis Receptor-mediated endocytosis is an important mechanism the body uses to remove cholesterol from the bloodstream. Persons with the inherited disease hypercholesterolemia lack normal LDL receptors and as a consequence, have dangerously high levels of circulating cholesterol. Their cells cannot remove circulating LDL particles, and so the load of cholesterol tends to accumulate on the walls of their arteries, which eventually blocks blood flow. Mammalian cells use receptor-mediated endocytosis to take in a wide variety of substances. In addition to LDL particles, for example, cells take in insulin and most other protein hormones by this process. Also, many of the immune system’s functions are dependent on receptor-mediated endocytosis. In each case, the substances that a cell takes in are restricted to molecules that can bind to the appropriate receptors on the plasma membrane. Clathrin coated pits play a role in many types of receptor-mediated endocytosis. In this coated pits, the cytoplasmic domains of the receptors interact with clathrin and allow the receptors and their ligands to be internalized. Receptor-mediated endocytosis of Low-Density Lipoprotein (LDL) Cell takes in a particle of low density lipoprotein, or LDL from the outside. To do this, the cell uses receptors that specifically recognize and bind to the LDL particle. The receptors are clustered together in a reinforced membrane structure called a coated pit. An LDL particle contains one thousand or more cholesterol molecules at its core. A monolayer of phospholipids surrounds the cholesterol core and is embedded with proteins called apo-B. These apo-B proteins are specifically recognized by receptors in the cell’s membrane. The receptors in the coated pit bind to the apo-B proteins on the LDL particle. The pit is reinforced by a lattice-like network of proteins called clathrin. Additional clathrin molecules then add to the lattice, which eventually pinches off a part of...
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