Single-strand break

Definition

A single-strand break (SSB) is a type of DNA damage where one of the two strands of the DNA double helix is severed, while the other strand remains intact. This form of damage can result from various factors, including exposure to ionizing radiation, certain chemicals, and normal cellular processes. SSBs are particularly significant because they can lead to more severe mutations or chromosomal abnormalities if not repaired properly.

5 Must Know Facts For Your Next Test

1. Single-strand breaks are primarily repaired by a process called base excision repair (BER), which involves removing damaged bases and restoring the DNA strand.
2. SSBs can occur spontaneously during DNA replication or as a result of environmental stressors like UV light and certain chemical agents.
3. Unlike double-strand breaks, single-strand breaks are less likely to result in catastrophic loss of genetic information, but they can still compromise genomic stability.
4. Failure to repair SSBs effectively can lead to mutations during DNA replication, as the polymerase may stall or incorporate incorrect nucleotides.
5. Certain proteins, like poly(ADP-ribose) polymerase (PARP), play a crucial role in sensing single-strand breaks and initiating repair processes.

Review Questions

• What are the key differences between single-strand breaks and double-strand breaks in DNA?
  • Single-strand breaks affect only one strand of the DNA helix, leaving the other strand intact, while double-strand breaks involve breaks in both strands. This distinction is critical because double-strand breaks pose a higher risk for genomic instability and loss of genetic information. Repair mechanisms for SSBs typically involve base excision repair, whereas double-strand breaks often require more complex repair pathways such as homologous recombination or non-homologous end joining.
• How do reactive oxygen species contribute to the occurrence of single-strand breaks in DNA?
  • Reactive oxygen species (ROS) are byproducts of normal cellular metabolism but can become harmful when their levels increase due to stress or environmental factors. They can interact with DNA, causing oxidation that leads to single-strand breaks. The oxidative damage disrupts the integrity of the DNA helix, which can trigger cellular repair mechanisms aimed at restoring the correct structure and preventing mutations during replication.
• Evaluate the implications of unrepaired single-strand breaks on cellular function and genomic stability.
  • Unrepaired single-strand breaks can lead to significant issues within a cell, particularly during DNA replication. If these breaks are not fixed, they may result in stalled replication forks or misincorporation of nucleotides, potentially causing mutations that could affect gene expression or lead to cell cycle dysregulation. Over time, accumulation of such mutations can contribute to tumorigenesis or other diseases, emphasizing the importance of efficient DNA repair mechanisms in maintaining genomic stability.

Related terms

double-strand break: A more severe type of DNA damage where both strands of the DNA helix are broken, leading to the potential loss of genetic information and increased risk of mutations.

DNA repair mechanisms: The cellular processes that detect and repair damaged DNA, ensuring the integrity and stability of the genome.

reactive oxygen species: Highly reactive molecules that can damage cellular components, including DNA, and are a common cause of single-strand breaks.