2006-09-11 09:36:50 · 4 answers · asked by narges 1 in Science & Mathematics ➔ Biology
Topoisomerases (type I: EC 5.99.1.2, type II: EC 5.99.1.3) are enzymes that act on the topology of DNA. The double-helical configuration that DNA strands naturally reside in makes them difficult to separate, and yet they must be separated by helicase proteins if other enzymes are to transcribe the sequences that encode proteins, or if chromosomes are to be replicated. In so-called circular DNA, in which double helical DNA is bent around and joined in a circle, the two strands are topologically linked, or knotted. Otherwise identical loops of DNA having different numbers of twists are topoisomers, and cannot be interconverted by any process that does not involve the breaking of DNA strands. Topoisomerases catalyze and guide the unknotting of DNA.
The insertion of viral DNA into chromosomes and other forms of recombination can also require the action of topoisomerases.
Many drugs operate through interference with the topoisomerases. The broad-spectrum fluoroquinolone antibiotics act by disrupting the function of bacterial type II topoisomerases. Some chemotherapy drugs work by interfering with topoisomerases in cancer cells: type 1 is inhibited by irinotecan and topotecan, while type 2 is inhibited by etoposide and teniposide.
2006-09-11 09:53:48 · answer #1 · answered by Glenn 2 · 0⤊ 0⤋
Topoisomerases are enzymes that change topology (supercoiling) of DNA by cutting one (topoisomerases type I) or both (topoisomerases type II) strands.
2006-09-11 16:55:36 · answer #2 · answered by srpkinja33 2 · 0⤊ 0⤋
It is an enzyme (protein) that helps relieve the tangling problems in the DNA double helix when replecation takes place..
2006-09-12 04:22:32 · answer #3 · answered by malaysia 2 · 0⤊ 0⤋
Enzymes that act on the DNA helix
2006-09-11 16:54:00 · answer #4 · answered by ...ジme 5 · 0⤊ 0⤋