Type II topoisomerases

Definition

Type II topoisomerases are enzymes that play a crucial role in DNA replication by introducing transient double-strand breaks in the DNA, allowing the strands to pass through one another and thus relieving torsional strain. This action is essential for managing the supercoiling that occurs ahead of the replication fork, enabling smoother progression during DNA synthesis in prokaryotes.

5 Must Know Facts For Your Next Test

1. Type II topoisomerases operate using an ATP-dependent mechanism to introduce double-strand breaks, allowing for the passage of another DNA segment through the break.
2. These enzymes are vital for preventing DNA tangling and maintaining proper DNA topology during the replication process.
3. Type II topoisomerases are target sites for certain antibiotics, such as fluoroquinolones, which inhibit their function and disrupt bacterial DNA replication.
4. In prokaryotes, the main type II topoisomerase is DNA gyrase, which specifically helps to introduce negative supercoils into the circular bacterial DNA.
5. Inhibition of type II topoisomerases can lead to increased DNA supercoiling and ultimately result in cell death due to failed replication.

Review Questions

• How do type II topoisomerases facilitate DNA replication in prokaryotes?
  • Type II topoisomerases facilitate DNA replication by introducing transient double-strand breaks in the DNA. This allows one segment of DNA to pass through another, which relieves torsional strain that builds up as the replication fork advances. By preventing tangling and maintaining proper DNA topology, these enzymes ensure that replication proceeds smoothly without interruptions.
• Discuss the specific role of DNA gyrase as a type II topoisomerase in bacterial cells.
  • DNA gyrase is a specific type II topoisomerase found in bacteria that plays a critical role in managing DNA supercoiling. It introduces negative supercoils into circular bacterial DNA, counteracting the positive supercoiling that occurs ahead of the replication fork. This function is essential for facilitating the unwinding of the double helix during replication and transcription processes, ultimately ensuring the integrity of genetic information.
• Evaluate the implications of targeting type II topoisomerases with antibiotics on bacterial cell survival and replication.
  • Targeting type II topoisomerases with antibiotics like fluoroquinolones has significant implications for bacterial cell survival. These antibiotics inhibit the function of enzymes like DNA gyrase, leading to an accumulation of unrelieved supercoils and resulting in replication stress. As a consequence, bacterial cells experience failure in DNA synthesis, ultimately leading to cell death. This targeted approach exploits a vital bacterial process, offering an effective strategy for combating infections.

Related terms

DNA gyrase: A specific type II topoisomerase found in prokaryotes that introduces negative supercoils into DNA, helping to relieve torsional stress during replication.

Supercoiling: The coiling of DNA strands upon themselves, which can create tension and hinder processes like replication and transcription.

Topoisomerase I: An enzyme that introduces single-strand breaks in DNA to relieve supercoiling, different from type II as it does not require ATP for its function.