The main difference between helicase and topoisomerase is that helicase unwinds the double-stranded DNA whereas topoisomerase relieves the tension created by helicase. Furthermore, helicase breaks the hydrogen bonds between the two DNA strands while topoisomerase breaks the phosphodiester linkages in the DNA backbone.
Helicase and topoisomerase are two enzymes involved in the DNA replication of both eukaryotes and prokaryotes. They play a key role in the separation of DNA strand by changing the topology of DNA.
Key Areas Covered
1. What is Helicase
– Definition, Types, Function
2. What is Topoisomerase
– Definition, Types, Function
3. What are the Similarities Between Helicase and Topoisomerase
– Outline of Common features
4. What is the Difference Between Helicase and Topoisomerase
– Comparison of Key Differences
Key Terms
DNA Helicase, RNA Helicase, Supercoils, Type I Topoisomerase, Type II Topoisomerase, Unwinding
What is Helicase
First of all, Helicase is an especial class of enzymes involved in almost all types of nucleic acid metabolism events including DNA replication, recombination, and DNA repair. It is also important in the transcription, RNA processing, translation, ribosome biogenesis, and decay. Moreover, the translocation along the nucleic acids as well as the function of helicases require energy derived from ATP. The main function of helicase is to unwind the double-stranded nucleic acids by breaking the hydrogen bonds between nucleotides. In some cases, helicases disrupt the protein-nucleic acid interactions as well. Due to the essential function of helicases, they become ubiquitous and evolutionary-conserved proteins.
Figure 1: Helicase and Topoisomerase in DNA Replication
In addition, there are two types of helicases as DNA helicase and RNA helicase. DNA helicase unwinds double-stranded DNA, which is an important function in the DNA replication. For instance, RNA helicase remodels both RNA and RNA-protein complexes during transcription, RNA splicing, and translation.
What is Topoisomerase
Topoisomerase is an enzyme responsible for the addition or removal of supercoils from the DNA duplex during DNA replication, transcription, chromatin remodelling, and recombination. It introduces single- or double-strand breaks to the DNA molecule. During DNA replication, helicases unwind the DNA duplex, introducing supercoils. The type I topoisomerases, which is one of the two types of topoisomerases, relax DNA by nicking one strand of the double-stranded DNA and rejoining it. Therefore, they remove the supercoils from the DNA duplex. Besides, the type II topoisomerase, which is the second type of topoisomerases, break both strands of DNA and rejoin it. However, the second type of topoisomerases can either introduce or remove supercoils from the DNA duplex.
Figure 2: DNA Topoisomerase IIA
Furthermore, the topoisomerases are functional in both the growing replication fork and in the chromosomes which have undergone DNA replication. Here, both types of topoisomerases can be further classified. The two main subtypes of the type I topoisomerases are the type IA topoisomerase and the type IB topoisomerase. Significantly, the type I topoisomerase do not use energy for the removal of supercoils, but the type II topoisomerase uses energy derived from ATP. The two main subtypes of the type II topoisomerases are type IIA topoisomerase and type IIB topoisomerase. DNA gyrase is an enzyme which belongs to the type IIA topoisomerase.
Similarities Between Helicase and Topoisomerase
- Helicase and topoisomerase are two enzymes involved in the DNA replication.
- Both enzymes occur in eukaryotes as well as prokaryotes.
- Also, both can act on DNA.
- Furthermore, the main function of these enzymes is to separate the double-stranded DNA molecule to facilitate the action of DNA polymerase.
Difference Between Helicase and Topoisomerase
Definition
Helicase refers to any of the enzymes that use the energy derived from the hydrolysis of nucleoside triphosphates to unwind the double-stranded helical structure of nucleic acids. Topoisomerase refers to a class of enzymes, which alter the supercoiling of double-stranded DNA. Thus, this is the main difference between helicase and topoisomerase.
Act on
Another difference between helicase and topoisomerase is that helicases act on both DNA and RNA while topoisomerases only act on DNA.
Function
Moreover, helicase breaks the hydrogen bonds between the double-stranded DNA while topoisomerase breaks the phosphodiester bonds between the nucleotides in the DNA backbone.
Role
Helicase unwinds the double-stranded DNA while topoisomerase relieves the tension generated by helicase. Hence, this is another difference between helicase and topoisomerase.
Types
The two types of helicases are the DNA helicase and RNA helicase while the two main types of topoisomerases are the type I topoisomerase and type II topoisomerase.
Conclusion
Helicase is an enzyme responsible for the unwinding of the nucleic acids during various types of metabolic events. Moreover, it breaks the hydrogen bonds between the double-stranded nucleic acids including both DNA and RNA. On the other hand, topoisomerase is an enzyme which can either introduce or remove supercoils from the DNA duplex. This is either by introducing single- or double-strand breaks. Therefore, the main difference between helicase and topoisomerase is the type of change in the topology of nucleic acids.
Reference:
1. Abdelhaleem M. Helicases: an overview. Methods Mol Biol. 2010;587:1–12. Available Here
2. Jankowsky, E., “RNA helicases at work: binding and rearranging” Trends in biochemical sciences vol. 36,1 (2011): 19-29. Available Here
3. Lodish H, Berk A, Zipursky SL, et al. Molecular Cell Biology. 4th edition. New York: W. H. Freeman; 2000. Section 12.3, The Role of Topoisomerases in DNA Replication. Available Here
Image Courtesy:
1. “Figure 14 04 01” By CNX OpenStax – (CC BY 4.0) via Commons Wikimedia
2. “1zxn” By Deposition authors: Wei, H., Ruthenburg, A.J., Bechis, S.K., Verdine, G.L.; visualization author: User:Astrojan – (CC BY 4.0) via Commons Wikimedia
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