Why Is The Fact That Water Moves Freely Through The Phospholipid Bilayer Unexpected?
The phospholipids that make up the phospholipid bilayer consist of a glycerol molecule bound to two fatty acids and one phosphate. The phosphate groups have negative charges while the fatty acids do not have any charge. The fatty acids are made of long chains of hydrogen and carbon atoms. Since hydrogen and carbon are similar in their electronegativity (their affinity for electrons), the fatty acids do not have significant polarity. Although there is no attraction between the fatty acid chains due to polarity, london dispersion forces do exist between the fatty acid chains. These forces hold the chains together so that the fatty acid ends of the phospholipids are oriented toward the interior of the membrane while the phosphate ends are oriented toward the surfaces of the membrane. Water molecules are extremely polar. This is a result of a large difference between the electronegativity of hydrogen and that of oxygen. Since there is such a large difference in their electronegativity, the
