DNA topoisomerase I

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DNA topoisomerases are enzymes that regulate the number of topological links between two DNA strands[1]. Topoisomerase I is an ATP-independant enzyme that catalyses the reaction of supercoiled DNA, cleaving one strand and creating conformational freedom. Topoisomerase I will bind to a DNA molecule and cleave one strand, simultaenously generating a phosphoester bond between the 5' free phosphate on the DNA and a tyrosine risdue found in the enzyme[2]. The free 3' hydorxyl of the DNA is noncovalently held by the enzyme. The strand that had not been cleaves passes thorugh sinle strand break, this causes the resealing of the cleaved strand of the DNA[3]. The newly resealed DNA strand has the exact chemical structure as it initially did prior form, the only difference that can be found it that the DNA strand has now one less negatively charged supercoil. 

Topoisomerase has different effects in eukaryotes and prokaryotes. In eukaryotes topoisomerase I enzymes are able to remove both positive and negative supercoils, whilst in prokaryotes they are only able to remove negative supercoils.

Refrences 

  1. EMBL-EBI IP. DNA Topoisomerase I, eukaryotic-type [Internet]. Interpro. EMBL-EBI; [cited 2017Dec4]. Available from: http://www.ebi.ac.uk/interpro/entry/IPR013499
  2. Lodish H. The Role of Topoisomerases in DNA Replication [Internet]. Molecular Cell Biology. 4th edition. U.S. National Library of Medicine; 1970 [cited 2017Dec4]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK21703/
  3. Lodish H. The Role of Topoisomerases in DNA Replication [Internet]. Molecular Cell Biology. 4th edition. U.S. National Library of Medicine; 1970 [cited 2017Dec4]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK21703/

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