Type II topoisomerase bound to DNA, Molecular model of human topoisomerase 2-alpha (blue, a form of type II topoisomerase) forming a complex with a strand of DNA (deoxyribonucleic acid, green and pink). The topoisomerase enzymes assist in uncoiling DNA. DNA is usually stored in a supercoiled form, which must be unravelled before it can be replicated or translated into proteins. Type I topoisomerase changes the linkage in multiples of one, while Type II changes the linkages in steps of two.