1. A turning inward, upside down, or in any direction contrary to the existing one. 2. Conversion of a disaccharide or polysaccharide by hydrolysis into a monosaccharide; specifically, the hydrolysis of sucrose to d-glucose and d-fructose; so called because of the change in optic rotation. 3. Alteration of a DNA molecule made by removing a fragment, reversing its orientation, and putting it back into place. 4. Heat-induced transition of silica, in which the quartz tridymite or cristobalite changes its physical properties as to thermal expansion. 5. Conversion of a chiral center into its mirror image.