Base excision repair

Definition

Base excision repair is a crucial cellular mechanism that fixes small, non-helix-distorting base lesions in DNA. This process is essential for maintaining genomic stability by removing damaged bases and replacing them with the correct ones, preventing mutations that could lead to diseases like cancer. It highlights the importance of repair systems in preserving DNA integrity during replication and cellular processes.

5 Must Know Facts For Your Next Test

1. Base excision repair primarily addresses damage caused by oxidation, alkylation, and deamination of bases, which can occur due to environmental factors or normal metabolic processes.
2. The process starts with DNA glycosylases recognizing and excising the damaged base, creating an AP site that is then processed by other enzymes.
3. After the AP site is formed, an endonuclease cuts the sugar-phosphate backbone, allowing for the removal of the sugar and subsequent filling of the gap by DNA polymerase.
4. Base excision repair is crucial for preventing mutations during DNA replication since unrepaired lesions can lead to permanent changes in the genetic code.
5. This repair mechanism works throughout the cell cycle but is particularly active during S phase when DNA replication occurs.

Review Questions

• How does base excision repair differ from other DNA repair mechanisms in terms of its specific targets?
  • Base excision repair specifically targets small, non-helix-distorting base lesions that arise from damage like oxidation or deamination. Unlike nucleotide excision repair, which deals with larger distortions such as bulky adducts, base excision repair focuses on correcting single bases without affecting the surrounding DNA structure. This specificity allows cells to efficiently maintain genomic integrity by quickly repairing minor damage that could otherwise accumulate and lead to mutations.
• Describe the steps involved in the base excision repair process and the roles of key enzymes.
  • The base excision repair process involves several key steps. First, a DNA glycosylase identifies and removes the damaged base, resulting in an AP site. Next, an endonuclease cuts the sugar-phosphate backbone at this site, facilitating the removal of the sugar. Subsequently, DNA polymerase fills in the gap with the correct nucleotide, followed by DNA ligase sealing the nicks in the sugar-phosphate backbone to restore the DNA strand fully. Each enzyme plays a critical role in ensuring accurate repair.
• Evaluate how base excision repair contributes to overall cellular health and its implications for cancer prevention.
  • Base excision repair is vital for maintaining cellular health by ensuring that small DNA damages are accurately repaired before they can lead to mutations during DNA replication. A robust base excision repair system reduces the likelihood of accumulating genetic errors that can drive oncogenesis. When this mechanism is compromised or defective, it increases susceptibility to mutations that can contribute to cancer development, highlighting its essential role in preventing malignant transformation and preserving genomic stability.

Related terms

DNA glycosylase: An enzyme that recognizes and removes damaged bases from DNA, initiating the base excision repair process.

AP site: A site in DNA that has lost a purine or pyrimidine base, often created during the base excision repair process.

DNA polymerase: An enzyme responsible for synthesizing new DNA strands by adding nucleotides during DNA replication and repair processes.