Topoisomerase

Definition

Topoisomerase is an essential enzyme that alters the topological states of DNA, helping to relieve the torsional strain that builds up ahead of the replication fork during DNA replication. By introducing transient breaks in the DNA strands, topoisomerases manage supercoiling and maintain proper DNA structure, which is critical for effective replication, transcription, and overall genomic stability.

5 Must Know Facts For Your Next Test

1. Topoisomerases are classified into two main types: Type I, which cuts one strand of DNA, and Type II, which cuts both strands, allowing for greater changes in topology.
2. In eukaryotic cells, topoisomerase II plays a crucial role during mitosis by resolving catenated chromosomes to ensure proper segregation.
3. Certain antibiotics target bacterial topoisomerases, like DNA gyrase, effectively inhibiting bacterial growth by preventing proper DNA replication.
4. Topoisomerases can be involved in DNA repair processes as they help maintain the integrity of the genome by resolving topological stress that may arise from damage.
5. Mutations or dysfunction in topoisomerases can lead to various diseases, including cancer, as they disrupt normal DNA replication and repair mechanisms.

Review Questions

• How do topoisomerases function in relieving torsional strain during DNA replication?
  • Topoisomerases function by introducing temporary breaks in the DNA strands, which allows them to unwind or relax the supercoiled structure. This process helps to alleviate the torsional strain that builds up ahead of the replication fork as the DNA unwinds. By managing supercoiling, topoisomerases ensure that the replication machinery can proceed smoothly along the template strand without encountering excessive tension or knots.
• Compare and contrast the roles of Type I and Type II topoisomerases in DNA replication and maintenance.
  • Type I topoisomerases cut one strand of the DNA double helix, allowing for relaxation of supercoils without requiring ATP energy. In contrast, Type II topoisomerases cut both strands and often introduce negative supercoils, requiring ATP for their action. While both types are essential for maintaining DNA topology during replication and other processes, Type II is particularly important for resolving catenated chromosomes during cell division.
• Evaluate the implications of targeting topoisomerases with specific drugs in cancer treatment and bacterial infections.
  • Targeting topoisomerases with specific drugs has significant implications for both cancer treatment and bacterial infections. In cancer therapy, drugs that inhibit topoisomerases can prevent rapidly dividing cells from successfully replicating their DNA, leading to cell death. Similarly, antibiotics that target bacterial topoisomerases effectively disrupt bacterial growth by hindering their ability to replicate DNA. However, care must be taken with these drugs as they can also affect normal cells and lead to side effects in patients.

Related terms

DNA gyrase: A type of topoisomerase found in bacteria that introduces negative supercoils into DNA, helping to alleviate the positive supercoiling that occurs ahead of the replication fork.

Supercoiling: The twisting of the DNA double helix upon itself, which can lead to strain and complications during processes such as replication and transcription.

Catenation: The intertwining of two or more circular DNA molecules, which can occur during DNA replication and must be resolved by topoisomerases to ensure proper chromosome segregation.