This picture is of the estrogen receptor bound to the HRE. The emphasized purple base pairs are mutated.  The sodium ions are represented as yellow spheres and the red spheres are the Zn ions. The H-bonds from the water are shown as Van der Walls forces. Although this picture doesn't show how the water can strengthen the binding, it does give us an better idea how a mutated base pair can easily weaken the binding of the receptor. The mutated base pair affects the energy inteactions between the DNA and the recptor.   TO THE TUTORIAL