bilayer confer on that bilayer a self-sealing property.Any tear in the Figure 11-11 A phospholipid bilayer bilayer will create a free edge with water,and because this is energeti- seen in cross-section.(A)Computer simu- cally unfavorable,the molecules of the bilayer will spontaneously re- lation showing the phospholipid mole- arrange to eliminate the free edge.If the tear is small,this spontaneous cules (red tails and yellow heads)and rearrangement will lead to the repair of the bilayer,restoring a single the surrounding water molecules(blue). (B)Schematic drawing of a phospholipid continuous sheet.If the tear is large,the sheet may break up into sepa- bilayer in water.(A,adapted from Science rate vesicles.In either case,the overriding principle is that free edges are 262:223-228(1993),courtesy of R.Venable quickly eliminated. and R.Pastor.) water bilaye water A (B) 1 nm