Unformatted text preview: They do this by changing the number of supercoils in the molecule, which without a change in the twist, would by definition would produce a change in the linking number. How can this happen? Topoisomerases create temporary breaks in the molecule, and once DNA is nicked or broken, the linking number can be altered. There is no inherent directionality to the action of topoisomerases, however. Supercoiling will change in either a positive or negative direction such that the potential energy of the molecule is minimized. Typically, a homogenous population of DNA molecules (i.e. all molecules have the same number of nucleotides and the same amount of supercoiling) will after treatment with a topoisomerase become more heterogeneous, with the formation of subpopulations that have differing degrees of supercoiling. This is illustrated in the gel that I showed in slide 24 of the DNA structure slides....
View Full Document
- Spring '08
- DNA, negative direction, supercoiling, closed circular molecules, closed circular molecule, circular prokaryotic genomes