5. Describe three differences between topoisomerase I and topoisomerase II. You
ID: 146642 • Letter: 5
Question
5. Describe three differences between topoisomerase I and topoisomerase II. You have an experiment in mind that requires topoisomerase I, but not topoisomerase 1, and would like to purify this enzyme from bacterial cells. Describe a purification strategy that would allow you to specifically isolate topoisomerase II relying on the unique activities of each enzyme. 6. RNA may fold back onto itself to form regions of double-stranded RNA. Describe at least two structures found in double-stranded regions of RNA. What features of RNA contribute to the stability of these double-stranded RNA regions? a. b.Explanation / Answer
Topoisomerases are enzymes that take part n the overwinding or underwinding of DNA. The winding problem of DNA arises due to the intertwined nature of its double helical structure.
The differences between Topoisomerase I and II can be listed as the following points--
*Topoisomerase I cut only one of the two strands of DNA, relax the strand and reanneal it. On the other hand, Topoisomerase II cuts both the strands of DNA simultaneously in order to manage DNA tangles and supercoils.
* Topoisomerase I do not require ATP for hydrolysis but Topoisomerase II needs to hydrolyze ATP.
* Topoisomerase I are subdivided into three sub-classes- Type I A, Type I B and Type I C which may differ from one another in structure and function.
Topoisomerase II is divided into two subclasses which possess similar structure and mechanism. They are Type IIa and Type II b.
6.a. The double strands formed in RNA are arranged in parallel [ unlike those of DNA, which are antiparallel ].
The double strands of RNA can form between two self-complementary regions of the same single
strand of RNA. Two RNAs which are known to have extensive double-stranded areas are tRNA and rRNA. Also, some riboviruses are known to have double-stranded RNA as genetic material.
b. RNAs are predominantly single-stranded and possess a ribose sugar which s characterized by the presence of the 2'-hydroxyl group on the pentose ring. This hydroxyl group makes RNA less stable than DNA because t can be hydrolyzed more easily.
Double-stranded RNA have hydrogen bonds between the parallel strands. The RNA helix formation is enthalpic and this makes it more stable.
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