DNA Structure and Replication

ID #2340

Are topoisomerase and helicase in the same group of enzymes or do they counteract each other's function?


Topoisomerases and helicases are not in the same group or family of enzymes. I wouldn't say that they necessarily counteract each other's functions as a general rule. Helicases unwind nucleic acids, often making them go from double-stranded to single-stranded (this is the only capacity in which we learn about helicases in MCB150). Topoisomerases can twist (or untwist) DNA that is already double-stranded. These two functions are quite independent of each other most of the time (e.g. supercoiling of prokaryotic DNA). During DNA replication, Helicase unwinds or opens up the DNA, making it single-stranded and creating a replication bubble. However, a strain (in the form of coils) are introduced at the ends of the "bubble", and this is where the Topoisomerase relieves the strain brought about by the extra twists on the double-stranded DNA. In this case, topoisomerase does counteract the effect of helicase, but they function very differently from each other. So no, they are not part of the same enzyme family. 

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