Single-strand breaks

Definition

Single-strand breaks are disruptions in the DNA structure where only one of the two strands is severed, leading to a temporary loss of integrity in the DNA helix. These breaks can occur due to various factors, including oxidative stress, radiation, and certain chemical agents. While they are less severe than double-strand breaks, if left unrepaired, single-strand breaks can compromise genomic stability and lead to mutations or cell death.

5 Must Know Facts For Your Next Test

1. Single-strand breaks can be repaired by multiple pathways, including base excision repair and nucleotide excision repair, highlighting the cell's ability to maintain DNA integrity.
2. If single-strand breaks are not repaired in a timely manner, they can result in more severe genetic damage, such as double-strand breaks during replication.
3. Certain environmental factors like UV radiation and chemicals found in cigarette smoke are known to induce single-strand breaks in DNA.
4. Cells utilize specialized enzymes called ligases to reconnect the broken ends of DNA after a single-strand break has occurred.
5. The accumulation of single-strand breaks over time can contribute to aging and increase the risk of cancer development due to genomic instability.

Review Questions

• How do single-strand breaks affect DNA replication and what mechanisms do cells use to repair them?
  • Single-strand breaks can impede DNA replication because the replication machinery requires an intact DNA strand to proceed. If a break occurs on one strand, it poses a risk during replication as the fork may collapse. Cells employ various repair mechanisms, primarily base excision repair and nucleotide excision repair, which involve recognizing the break, excising damaged regions, and accurately restoring the DNA structure to ensure continued genomic integrity.
• Discuss the implications of unrepairable single-strand breaks in the context of cellular health and potential disease development.
  • Unrepairable single-strand breaks can lead to significant cellular health issues. When these breaks persist, they can result in double-strand breaks during cell division or replication, ultimately causing mutations. The accumulation of mutations can disrupt essential cellular functions and contribute to diseases such as cancer by promoting uncontrolled cell growth or apoptosis. Therefore, effective repair mechanisms are crucial for maintaining cellular health and preventing disease onset.
• Evaluate how oxidative stress contributes to single-strand breaks and the potential long-term effects on cellular function and organismal health.
  • Oxidative stress plays a major role in inducing single-strand breaks due to an excess of free radicals that can react with DNA. This interaction often results in damage that compromises DNA integrity. Over time, persistent oxidative stress leading to accumulated single-strand breaks can impair cellular functions like transcription and replication. This impairment is associated with aging processes and age-related diseases, emphasizing the need for antioxidant defenses and efficient DNA repair pathways to maintain organismal health.

Related terms

DNA Repair Mechanisms: The processes by which a cell identifies and corrects damage to its DNA, essential for maintaining genetic stability.

Base Excision Repair: A DNA repair pathway that corrects single-strand breaks by removing damaged bases and replacing them with the correct nucleotides.

Oxidative Stress: An imbalance between free radicals and antioxidants in the body, which can lead to cellular damage, including DNA breaks.