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How do LDL receptors help body cells take cholesterol out of the bloodstream?
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Lipid
Structure and properties of two representative lipids. Both stearic acid (a fatty acid) and phosphatidylcholine (a phospholipid) are composed of chemical groups that form polar “heads” and nonpolar “tails.” The polar heads are hydrophilic, or soluble in water, whereas the nonpolar tails are hydrophobic, or insoluble in water. Lipid molecules of this composition spontaneously form aggregate structures such as micelles and lipid bilayers, with their hydrophilic ends oriented toward the watery medium and their hydrophobic ends shielded from the water.
Body cells extract cholesterol from the bloodstream through a specialized process involving low-density lipoprotein (LDL) receptors located on the cell surface.12
The mechanism functions as follows:
- Recognition: The LDL particle contains a specific protein called apoB-100. The LDL receptor on the surface of a recipient cell recognizes and binds to this apoprotein.2
- Internalization: Once the LDL particle is bound to the receptor, the cell engulfs the entire receptor-LDL complex in a process known as [endocytosis].2
- Processing: After the complex is drawn into the cell, the LDL particle releases its cholesterol contents. The apoB-100 protein is subsequently degraded into amino acids, which the cell uses for protein synthesis or as an energy source.2
This process is tightly regulated; when a cell has sufficient cholesterol, it inhibits the production of more LDL receptors on its surface, thereby limiting further cholesterol intake. Defects in these receptors can prevent cholesterol from entering cells, causing it to accumulate in the blood and leading to conditions such as atherosclerosis and familial hypercholesterolemia.134