Type I topoisomerases

Definition

Type I topoisomerases are enzymes that introduce single-strand breaks in DNA, allowing for the relaxation of supercoiled DNA without the need for ATP. They are crucial during DNA replication in prokaryotes as they help to alleviate the torsional strain that accumulates ahead of the replication fork, ensuring that DNA unwinding can proceed smoothly. By temporarily breaking one strand of the DNA helix and then rejoining it, these enzymes play a vital role in maintaining the structural integrity of DNA during replication and other cellular processes.

5 Must Know Facts For Your Next Test

1. Type I topoisomerases cut one strand of the DNA helix to relieve tension caused by supercoiling during replication.
2. They are classified into two subtypes: Type IA, which relaxes negative supercoils, and Type IB, which relaxes both negative and positive supercoils.
3. These enzymes function by creating a transient single-strand break, allowing the unbroken strand to pass through before resealing the break.
4. In prokaryotes, Type I topoisomerases are essential for ensuring that DNA replication proceeds efficiently without excessive twisting or tangling.
5. Inhibition of Type I topoisomerases can lead to problems in DNA replication and ultimately cell death, making them potential targets for antibacterial drugs.

Review Questions

• How do Type I topoisomerases contribute to the process of DNA replication in prokaryotes?
  • Type I topoisomerases play a crucial role in DNA replication by alleviating the torsional strain that occurs as the double helix unwinds at the replication fork. By introducing single-strand breaks in the DNA, these enzymes allow for the relaxation of supercoiled regions that build up due to the unwinding process. This action ensures that the replication machinery can move smoothly along the DNA without encountering excessive tension, facilitating proper synthesis of new DNA strands.
• Compare and contrast Type I and Type II topoisomerases in terms of their mechanisms and roles during DNA replication.
  • Type I topoisomerases introduce single-strand breaks in DNA to relieve supercoiling, while Type II topoisomerases create double-strand breaks to allow one double-stranded segment to pass through another. Type I enzymes typically relax supercoiled DNA by cutting one strand and allowing it to swivel around the unbroken strand, whereas Type II enzymes manage higher-order supercoiling by enabling segment passage. Both types are essential for maintaining DNA structure and function during replication, but they operate on different aspects of DNA topology.
• Evaluate the potential consequences of inhibiting Type I topoisomerases in bacterial cells during DNA replication.
  • Inhibiting Type I topoisomerases in bacterial cells can lead to severe complications during DNA replication. Without the ability to relieve torsional strain caused by supercoiling, replicating DNA may become excessively twisted and tangled. This could result in stalled replication forks and ultimately lead to incomplete or erroneous DNA synthesis. The inability to properly manage DNA topology would likely trigger cell stress responses and could culminate in cell death, making these enzymes attractive targets for developing new antibacterial therapies.

Related terms

DNA supercoiling: The over- or under-winding of a DNA strand, which can create torsional strain during processes like replication and transcription.

Type II topoisomerases:

Enzymes that introduce double-strand breaks in DNA, allowing for the passage of another double strand through the break to relieve tension caused by supercoiling.

Replication fork: The Y-shaped region that forms when DNA is being unwound and replicated, consisting of two single strands of DNA being synthesized.