Topoisomerase

Definition

Topoisomerase is an essential enzyme that regulates the overwinding or underwinding of DNA strands during processes like replication and transcription. By introducing or removing twists in the DNA helix, topoisomerases ensure that the DNA can be properly accessed and unwound for the synthesis of new strands or the production of RNA. This activity is crucial for maintaining the integrity and function of the genetic material.

5 Must Know Facts For Your Next Test

1. Topoisomerases can be categorized into two main types: Type I, which cuts one strand of DNA, and Type II, which cuts both strands.
2. Type II topoisomerases are crucial during DNA replication because they help manage the tension created ahead of the replication fork.
3. In transcription, topoisomerases relieve torsional strain that builds up as RNA polymerase moves along the DNA template.
4. Some antibiotics target bacterial topoisomerases to inhibit their function, effectively stopping bacterial replication and growth.
5. Topoisomerase enzymes are highly conserved across species, indicating their fundamental role in cellular processes.

Review Questions

• How does topoisomerase function to maintain DNA structure during replication?
  • Topoisomerase maintains DNA structure during replication by relieving the torsional strain that builds up ahead of the replication fork. As helicase unwinds the DNA, it creates supercoiling, which can hinder further unwinding. Topoisomerases alleviate this strain by cutting the DNA strands, allowing them to unwind or rewind properly before resealing them. This action is vital for ensuring smooth progression of the replication process.
• Discuss the role of topoisomerase in transcription and why it is necessary for gene expression.
  • In transcription, topoisomerase plays a critical role by managing the supercoiling that occurs as RNA polymerase synthesizes RNA from the DNA template. As RNA polymerase moves along the DNA, it causes localized overwinding ahead of it and underwinding behind it. Topoisomerase resolves these tensions by introducing or removing twists in the DNA helix, which ensures that RNA polymerase can progress efficiently and accurately through the gene being expressed.
• Evaluate how inhibiting topoisomerase activity could impact both prokaryotic and eukaryotic cells differently.
  • Inhibiting topoisomerase activity in prokaryotic cells can lead to lethal consequences as these cells rely on topoisomerases for essential functions such as DNA replication and repair. Antibiotics that target bacterial topoisomerases can effectively halt bacterial growth. In eukaryotic cells, while inhibiting topoisomerases can also impede cell division and growth, these cells have multiple types of topoisomerases and additional mechanisms for managing DNA stress. This may lead to different outcomes regarding cell viability and potential development of resistance over time.

Related terms

DNA helicase:

An enzyme responsible for unwinding the DNA double helix ahead of the replication fork to allow access for other enzymes.

RNA polymerase:

An enzyme that synthesizes RNA from a DNA template during transcription, playing a critical role in gene expression.

supercoiling: The coiling of the DNA molecule upon itself due to torsional stress, which can affect processes like replication and transcription.