Nucleotide excision repair

Definition

Nucleotide excision repair is a cellular mechanism that identifies and corrects damaged DNA by removing a short segment of nucleotides around the lesion and replacing it with the correct sequence. This process plays a crucial role in maintaining genomic integrity, particularly in response to DNA damage caused by environmental factors like UV radiation and certain chemicals.

5 Must Know Facts For Your Next Test

1. Nucleotide excision repair can remove a variety of DNA lesions, including those caused by UV-induced thymine dimers, which are common forms of DNA damage.
2. The process involves several steps: recognition of the damage, excision of the damaged DNA strand, synthesis of a new strand using the undamaged template, and ligation to seal the remaining gaps.
3. Deficiencies in nucleotide excision repair can lead to genetic disorders such as Xeroderma Pigmentosum, which increases susceptibility to skin cancer due to an inability to repair UV-induced DNA damage.
4. The mechanism relies on multiple proteins and enzymes, including damage recognition proteins, endonucleases for cutting the damaged strand, and DNA polymerase for filling in the gaps.
5. Nucleotide excision repair is conserved across many organisms, highlighting its fundamental importance in cellular biology and its evolutionary significance in maintaining genome stability.

Review Questions

• How does nucleotide excision repair recognize and correct specific types of DNA damage?
  • Nucleotide excision repair recognizes DNA damage through specialized proteins that detect distortions in the DNA helix. Once a lesion, such as a thymine dimer from UV radiation, is identified, the repair mechanism initiates excision of a short segment surrounding the damage. This allows the cell to synthesize a new DNA strand using the undamaged template as a guide, effectively restoring the correct sequence.
• Discuss the implications of defective nucleotide excision repair mechanisms on human health and disease.
  • Defective nucleotide excision repair mechanisms can have severe health implications, as they lead to an accumulation of unrepaired DNA damage. For instance, conditions like Xeroderma Pigmentosum result from mutations in genes involved in this repair pathway. Individuals with this disorder exhibit extreme sensitivity to sunlight and a dramatically increased risk of developing skin cancers due to their inability to efficiently repair UV-induced DNA lesions.
• Evaluate the role of nucleotide excision repair in preserving genome stability and preventing mutations across different organisms.
  • Nucleotide excision repair plays a vital role in preserving genome stability by efficiently correcting various forms of DNA damage that can otherwise lead to mutations. By eliminating damaged nucleotides and replacing them with the correct sequence, this repair mechanism minimizes the risk of errors during DNA replication. Its conservation across many organisms underscores its evolutionary importance; organisms with effective repair systems have better chances of survival against environmental stressors that cause genetic damage.

Related terms

DNA damage: Any alteration to the DNA structure that affects its integrity, often caused by external agents such as UV light, radiation, or chemical exposure.

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

mutation:

A permanent alteration in the DNA sequence that can result from DNA damage or errors during replication, potentially leading to functional changes in proteins.