Nucleotide excision repair

Definition

Nucleotide excision repair is a DNA repair mechanism that removes and replaces damaged segments of DNA, particularly those caused by UV light or chemical exposure. This process is crucial for maintaining the integrity of genetic material and ensuring accurate DNA replication, helping to prevent mutations that could lead to diseases such as cancer.

5 Must Know Facts For Your Next Test

1. Nucleotide excision repair operates through a series of steps: damage recognition, strand incision, excision of the damaged segment, synthesis of a new segment, and ligation to restore the DNA strand.
2. This repair mechanism is essential for fixing bulky DNA adducts and lesions that disrupt normal base pairing and hinder proper replication.
3. Proteins involved in nucleotide excision repair include the XP (Xeroderma pigmentosum) proteins, which are essential for recognizing and repairing UV-induced damage.
4. Mutations in genes encoding nucleotide excision repair proteins can lead to disorders such as Xeroderma pigmentosum, characterized by increased sensitivity to sunlight and a higher risk of skin cancer.
5. Nucleotide excision repair is a highly conserved process across various organisms, highlighting its importance in cellular function and genome stability.

Review Questions

• How does nucleotide excision repair contribute to maintaining genetic stability during DNA replication?
  • Nucleotide excision repair plays a vital role in maintaining genetic stability by identifying and correcting DNA damage before replication occurs. By removing bulky lesions such as thymine dimers caused by UV exposure, this repair mechanism ensures that the DNA template remains intact for accurate replication. Without effective nucleotide excision repair, mutations could accumulate during replication, leading to potential cellular dysfunction or diseases like cancer.
• Discuss the steps involved in the nucleotide excision repair process and how each step contributes to repairing damaged DNA.
  • The nucleotide excision repair process involves several key steps: first, damage recognition occurs when specific proteins identify distortions in the DNA helix. Next, two incisions are made around the damaged segment, allowing the removal of a short stretch of nucleotides containing the lesion. After excision, DNA polymerase synthesizes new nucleotides to fill the gap, and finally, DNA ligase seals the new segment into place. Each step is crucial for ensuring that the original genetic information is restored accurately.
• Evaluate the implications of defective nucleotide excision repair mechanisms on human health, particularly concerning skin cancer risk.
  • Defective nucleotide excision repair mechanisms can have severe implications for human health, particularly regarding skin cancer. For instance, individuals with mutations in genes responsible for this repair process are at higher risk for disorders like Xeroderma pigmentosum. In these cases, inability to properly fix UV-induced DNA damage leads to an accumulation of mutations in skin cells, increasing susceptibility to skin cancers. Understanding these connections emphasizes the importance of effective DNA repair mechanisms in preventing carcinogenesis.

Related terms

DNA polymerase:

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

Thymine dimers: Covalent linkages formed between adjacent thymine bases in DNA due to UV radiation, leading to distortions in the DNA structure that can cause replication errors.

Base excision repair: A DNA repair pathway that removes and replaces damaged or non-canonical bases in the DNA, involving specific glycosylases and AP endonucleases.