Submit Article |Resources | Link to us | Sitemap | Search | Language
Back to Home
Home >> DNA Replication and Repair >> Topoisomerase
Back to Home

Topoisomerase -This enzyme is responsible for the prevention of torsion force created on DNA due to helicase action. Topoisomerase can release a supercoiled DNA but cannot coil a DNA. Topoisomerase may be divided into two classes depending upon the cleavage mode.

Tspe I DNA topoisomerase
 This enzyme is responsible for prevention of torsion force created on DNA. It reversibly cuts a single strand of the double helix. It has both nuclease and ligase (strand-resealing) activities. This enzyme does not require ATP, but rather appears to store the energy from the phosphodiester bond it cleaves reusing the energy to reseal the strand.

By creating a transient "nick", the DNA helix on either side of the nick is allowed to rotate at the phosphodiester bond opposite the nick, thus relieving accumulated supercoils.

Type 1 topoisomerase relaxes negative supercoils (that is, those that contain fewer turns of the helix than relaxed DNA) in prokaryotes. But it can cleave both negative and positive supercoils (that is, those that contain more turns of the helix than relaxed DNA) in eukaryotic cells.

Type II DNA topoisomerase

This enzyme binds tightly to the DNA double helix and makes transient breaks in both strands. The enzyme then causes a second strand of the DNA double helix to pass through the break and finally reseals the break. As a result, both negative and positive supercoils can be relieved.

Type II DNA topoisomerase is required in both prokaryotes and eukaryotes for the separation of interlocked molecules of DNA following chromosomal replication. This topoisomerase also does not require ATP.

 
   
Submit Article |Resources | Link to us | Sitemap | Search | Language
English|Français|Español|Deutsch|Italiano|Portugues|Japanese|Korean|Sim-Chinese| Language