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LDL receptors on cell membrane, illustration. The binding of LDL (low-density lipoprotein) droplets (spherical lipid particles) to the LDL receptors (green/orange, centre) results in the endocytosis of this biochemical molecule through the cell membrane into clathrin-coated vesicles (right-hand side), which are then processed inside the cell. LDL droplets consist of a core of esterified cholesterol molecules surrounded by a shell of unesterified cholesterol and phospholipids. High blood levels of LDL ('bad') cholesterol compared to HDL (high-density lipoprotein) cholesterol are thought to raise the risk of atherosclerosis, the build-up of fatty deposits on artery walls. This is a major cause of heart attacks and strokes.