Topoisomerase

Definition

Topoisomerase is an enzyme that plays a critical role in the manipulation of DNA topology by introducing or removing supercoils in the DNA molecule. This process is essential for DNA replication and transcription, as it helps to alleviate the torsional strain that builds up ahead of the replication fork or during RNA synthesis. By modifying the supercoiling of DNA, topoisomerases ensure that the DNA strands remain accessible for the necessary cellular processes.

5 Must Know Facts For Your Next Test

1. Topoisomerases are classified into two main types: Type I topoisomerases, which cut one strand of DNA to relieve supercoiling, and Type II topoisomerases, which cut both strands to introduce or remove twists.
2. In eukaryotes, topoisomerase II is vital during the S phase of the cell cycle when DNA is replicated, helping to manage the tension created by unwinding DNA strands.
3. Topoisomerases are essential not only for DNA replication but also for processes like transcription and chromosome segregation during cell division.
4. Certain drugs targeting topoisomerases, such as chemotherapy agents, exploit their function to induce breaks in DNA, which can lead to cancer cell death.
5. Mutations or malfunctions in topoisomerases can result in genomic instability, contributing to various diseases including cancer.

Review Questions

• How do topoisomerases facilitate the processes of DNA replication and transcription?
  • Topoisomerases facilitate DNA replication and transcription by alleviating torsional strain that occurs when the double helix is unwound. As helicase unzips the DNA, supercoiling develops ahead of the fork due to overwinding. Topoisomerases cut and rejoin the DNA strands, allowing it to unwind and preventing tangling or breakage, which is crucial for maintaining the integrity of genetic information during these processes.
• What are the differences between Type I and Type II topoisomerases in terms of their mechanisms and functions?
  • Type I topoisomerases act by cutting one strand of the DNA helix, allowing it to rotate around the other strand to relieve supercoiling without needing ATP. In contrast, Type II topoisomerases cut both strands simultaneously and require ATP for their function, enabling them to introduce or remove two supercoils at once. This distinction is important for understanding how different types manage DNA topology under varying cellular conditions.
• Evaluate the role of topoisomerases in maintaining genomic stability and their implications in cancer treatment.
  • Topoisomerases play a crucial role in maintaining genomic stability by managing DNA supercoiling during critical processes like replication and transcription. When these enzymes malfunction or are inhibited, it can lead to genomic instability, which is a hallmark of cancer cells. Understanding this relationship has led to the development of targeted therapies that inhibit specific topoisomerases, effectively inducing breaks in cancer cell DNA and promoting cell death. This strategy highlights how fundamental cellular processes can be exploited in therapeutic contexts.

Related terms

DNA supercoiling: The coiling of the DNA double helix upon itself, which can occur in overwound (positive) or underwound (negative) forms, affecting how DNA is accessed for replication and transcription.

helicase:

An enzyme responsible for unwinding the DNA double helix ahead of the replication fork, creating single-stranded regions necessary for replication and transcription.

DNA ligase: An enzyme that facilitates the joining of DNA strands together by catalyzing the formation of phosphodiester bonds, playing a crucial role in DNA repair and replication.