DNA topoisomerase

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DNA topoisomerase plays an impotant role in breaking the phosphodiester bond by binding covalently onto the DNA backbone phosphate. It acst as a reversible nuclease. This whole process is a reversible one, whereby before the protein leaves, the phosophodiester bonds are re-made. There are two types of DNA topoisomerase, topoisomerase I and topoismerase II[1].

Topoisomerase I

Topoisomerase I catalyses the cleavage of the double stranded DNA by relaxing the supercoiled DNA. This process releases energy, as it is thermodynamically favourable [2].

Topoisomerase II

Topoisomerase II (also called gyrase) cleaves the double-stranded DNA by adding negative supercoils to DNA. Duplex DNA requires unrestricted rotation when replicating, so a swivel mechanism exists to prevent stress building up on the duplex further along and possibly inhibiting strand separation. This mechanism of relieving stress is facilitated by toposimerase II (gyrase). Its method of action involves cleaving dsDNA, rotating the ends of these broken strands, thereby relieving torsional stress, and re-joining the strands.   This process hydrolyses ATP to produce the required energy [3].

Reference

  1. Alberts, BA, 2008. Molecular Biology of The Cell. 5th ed. New York: Garland Science.
  2. Berg, J., Tymoczko, J., Stryer, L. and Berg, J. (2011). Student companion for Biochemistry, 7th edition, international edition. 1st ed. New York: W.H. Freeman.
  3. Berg, J., Tymoczko, J., Stryer, L. and Berg, J. (2011). Student companion for Biochemistry, 7th edition, international edition. 1st ed. New York: W.H. Freeman.


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