Difference Between Helicase and Topoisomerase

The key difference between helicase and topoisomerase is that helicase is an enzyme that separates two complementary strands of DNA by breaking hydrogen bonds between the bases of two strands while topoisomerase is an enzyme that removes positive and negative supercoils formed during the unwinding process of DNA by cutting and resealing one or both strands of the DNA duplex.

DNA is a double helix. It exists in two complementary strands bonded together via hydrogen bonds. DNA replication, transcription and DNA repairing require two strands to be separated from each other to make new copies, make mRNA and add nucleotides to repair. The two enzymes helicase and topoisomerase come into play at this point. Therefore, both helicase and topoisomerases are essential in DNA unwinding. Helicase separates double-stranded DNA into single strands by breaking the hydrogen bonds between the nucleotide base pairs in double-stranded DNA. In contrast, topoisomerase unravels the DNA twist and relieves the DNA supercoil nature by cutting the DNA phosphate backbone either in one or both strands.

CONTENTS

1. Overview and Key Difference
2. What is Helicase 
3. What is Topoisomerase
4. Similarities Between Helicase and Topoisomerase
5. Side by Side Comparison – Helicase vs Topoisomerase in Tabular Form
6. Summary

What is Helicase?

Helicase is an essential enzyme during DNA replication, transcription, recombination and repair. Helicase is able to break hydrogen bonds existing between the bases of two complementary strands of DNA helix. To separate two strands, helicase binds with the DNA at the place where the synthesis of new strand initiates. It creates a replication fork and initiates breaking of hydrogen bonds one by one.  Helicase utilizes the energy of ATP for its activity.

In addition to the above, there are DNA helicases as well as RNA helicases. RNA helicases assist all the processes of RNA, including transcription, splicing, and translation, RNA transport, RNA editing, etc.

What is Topoisomerase?

Topoisomerase is an enzyme that cuts DNA at a particular point and unravels the DNA twist and relieves the DNA supercoil nature. During the helicase action, supercoiling of DNA takes place due to the intertwined structure of double-stranded DNA. These types of topological problems created in the DNA doubled strands can be corrected by topoisomerases. They usually cut the DNA phosphate backbone either in one or both strands and allow the DNA supercoil structure to be unwound. Later, topoisomerase seals DNA backbone again.

Topoisomerase I and II are two types of topoisomerases that deal with supercoiled DNA. Topoisomerase I cuts one strand in the double-stranded DNA without utilizing energy. In contrast, topoisomerase II cuts both strands in DNA, utilizing ATP for its activity. Due to the topoisomerase activity, DNA is able to undergo replication, transcription, repair and chromosomal segregation, etc.

What are the Similarities Between Helicase and Topoisomerase?

• Helicase and topoisomerase are two enzymes needed for DNA replication, transcription and repair.
• Both enzymes aid in unwinding double-stranded DNA.

What is the Difference Between Helicase and Topoisomerase?

Helicase enzyme breaks hydrogen bonds between the bases of two complementary strands of DNA or RNA and separates two strands from each other. On the other hand, topoisomerase enzyme alters the supercoiling of double-stranded DNA by cutting phosphate backbone of either in one strand or double strands. So, this is the key difference between helicase and topoisomerase. Furthermore, helicase acts on both DNA and RNA, while topoisomerase acts only on DNA. Therefore, this is another difference between helicase and topoisomerase.

Summary – Helicase vs Topoisomerase

Helicase is an enzyme that separates annealed two strands of DNA, RNA or DNA-RNA hybrid by breaking hydrogen bonds between bases. It carries out its function by utilizing energy.  In contrast, topoisomerase is an enzyme that creates single-stranded or double-stranded breaks to relieve stress during supercoiling. So, this is the key difference between helicase and topoisomerase. Both enzymes are important in DNA replication, transcription and repair.

Reference:

1. “helicase.” Nature News, Nature Publishing Group, Available here.
2. Lodish, Harvey. “The Role of Topoisomerases in DNA Replication.” Molecular Cell Biology. 4th Edition., U.S. National Library of Medicine, 1 Jan. 1970, Available here.

Image Courtesy:

1. “0323 DNA Replication” By OpenStax – (CC BY 4.0) via Commons Wikimedia
2. “Topoisomerase Inhibitor” By Vtvu – Own work (CC BY-SA 3.0) via Commons Wikimedia