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Cell survival depends on balancing water uptake and loss

Cell survival depends on balancing water uptake and loss -...

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Cell survival depends on balancing water uptake and loss. An animal cell (or other cell without a cell wall) immersed in an isotonic environment  experiences no net movement of water across its plasma membrane. Water molecules move across the membrane but at the same rate in both directions. The volume of the cell is stable. The same cell in a hypertonic environment will lose water, shrivel, and probably die. A cell in a hypotonic solution will gain water, swell, and burst. Receptor-mediated endocytosis  allows greater specificity, transporting only certain  substances. This process is triggered when extracellular substances, or  ligands,  bind to special receptors  on the membrane surface. The receptor proteins are clustered in regions of the membrane  called coated pits, which are lined on their cytoplasmic side by a layer of coat proteins.
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Unformatted text preview: Binding of ligands to receptors triggers the formation of a vesicle by the coated pit, bringing the bound substances into the cell. Receptor-mediated endocytosis enables a cell to acquire bulk quantities of specific materials that may be in low concentrations in the environment. Human cells use this process to take in cholesterol for use in the synthesis of membranes and as a precursor for the synthesis of steroids. Cholesterol travels in the blood in low-density lipoproteins (LDL), complexes of protein and lipid. These lipoproteins act as ligands to bind to LDL receptors and enter the cell by endocytosis. In an inherited disease called familial hypercholesterolemia, the LDL receptors are defective, leading to an accumulation of LDL and cholesterol in the blood. This contributes to early atherosclerosis....
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