Topoisomerases (type I: EC number [http://www.expasy.org/cgi-bin/nicezyme.pl?5.99.1.2 5.99.1.2], type II: EC number [http://www.expasy.org/cgi-bin/nicezyme.pl?5.99.1.3 5.99.1.3]) are enzymes that act on the knot theory of DNA. The Double helix 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 transcription the DNA sequence that genetic code proteins, or if chromosomes are to be replication. 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 Knot theory. Otherwise identical loops of DNA having different numbers of twists are Topoisomer, 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 Quinolone antibiotics act by disrupting the function of bacterial type II topoisomerases. Some chemotherapy drugs work by interfering with topoisomerases in cancer Cell (biology): type 1 is inhibited by irinotecan and topotecan, while type 2 is inhibited by etoposide and teniposide. ==Type I topoisomerases== Both type I and type II topoisomerases change the Supercoil of DNA. Type I topoisomerases function by nicking one of the strands of the DNA double helix, twisting it around the other strand, and religating the nicked strand. Type I topisomerases change the linking number of a circular DNA strand by 1. ==Type II topoisomerases== Type II topoisomerases cut both strands of the DNA helix simultaneously. One free end is twisted, and the severed strands are reattached. Type II topoisomerases change the linking number of a DNA loop by 2. For example, DNA gyrase is a type II isomerase observed in E. coli and most other Prokaryote. Gyrase introduces negative supercoils and decreases the link number by 2. Gyrase is able to relieve knots in the Chromosome. ==See also== * DNA topology * Supercoil * Moebius Strip EC 5.99.1
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Topoisomerase
Topoisomerase
Topoisomerases (type I: EC number [http://www.expasy.org/cgi-bin/nicezyme.pl?5.99.1.2 5.99.1.2], type II: EC number [http://www.expasy.org/cgi-bin/nicezyme.pl?5.99.1.3 5.99.1.3]) are enzymes that act on the knot theory of DNA. The Double helix 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 transcription the DNA sequence that genetic code proteins, or if chromosomes are to be replication. 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 Knot theory. Otherwise identical loops of DNA having different numbers of twists are Topoisomer, 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 Quinolone antibiotics act by disrupting the function of bacterial type II topoisomerases. Some chemotherapy drugs work by interfering with topoisomerases in cancer Cell (biology): type 1 is inhibited by irinotecan and topotecan, while type 2 is inhibited by etoposide and teniposide. ==Type I topoisomerases== Both type I and type II topoisomerases change the Supercoil of DNA. Type I topoisomerases function by nicking one of the strands of the DNA double helix, twisting it around the other strand, and religating the nicked strand. Type I topisomerases change the linking number of a circular DNA strand by 1. ==Type II topoisomerases== Type II topoisomerases cut both strands of the DNA helix simultaneously. One free end is twisted, and the severed strands are reattached. Type II topoisomerases change the linking number of a DNA loop by 2. For example, DNA gyrase is a type II isomerase observed in E. coli and most other Prokaryote. Gyrase introduces negative supercoils and decreases the link number by 2. Gyrase is able to relieve knots in the Chromosome. ==See also== * DNA topology * Supercoil * Moebius Strip EC 5.99.1
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Topoisomerase
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