Assume the following: The total area of cell membrane in a single fat cell is 104 mm2, there is one insulin receptor per 1 mm2 of membrane, and 1 mm2 of cell membrane contains 106 phospholipid molecules.
1. How many insulin receptors are in a fat cell?
2. How many phospholipids molecules are in a fat cell?
3. How many phospholipid molecules are there for each insulin receptor?
4. What general principle of hormone action does your answer support?
1. 1 receptor/1 mm2 × 10 4 mm2/cell = 10 4 receptors per cell.
2. 104 mm2/cell × 10 6 phospholipids/mm2 = 10 10 phospholipid molecules per cell.
3. (1010 phospholipids/cell) / (104 receptors/cell) = 10 6 phospholipid molecules per insulin receptor.
4. Hormones exert their effects at very low concentrations (therefore it is not surprising that the hormone receptors,
through which the hormones act, are also in low concentration).
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