Cyclobutane pyrimidine dimers

Definition

Cyclobutane pyrimidine dimers (CPDs) are a type of DNA lesion formed when two adjacent pyrimidine bases, typically thymine, become covalently bonded due to exposure to ultraviolet (UV) light. These dimers distort the DNA structure, leading to replication errors and potential mutations if not repaired, making them critical in the study of DNA repair mechanisms.

5 Must Know Facts For Your Next Test

1. Cyclobutane pyrimidine dimers are one of the most common forms of UV-induced DNA damage, primarily occurring in skin cells due to sun exposure.
2. If left unrepaired, CPDs can lead to errors during DNA replication, potentially resulting in mutations that contribute to skin cancer development.
3. Nucleotide excision repair is the primary mechanism by which cells recognize and repair CPDs, involving several proteins that work together to remove the damaged DNA.
4. Photolyase enzymes play a crucial role in photoreactivation, specifically targeting CPDs and reversing their formation in the presence of light.
5. The efficiency of DNA repair mechanisms can vary among different organisms, influencing their susceptibility to UV-induced damage and the formation of cyclobutane pyrimidine dimers.

Review Questions

• How do cyclobutane pyrimidine dimers affect DNA replication and what consequences might arise from these effects?
  • Cyclobutane pyrimidine dimers cause a distortion in the DNA structure, which can hinder proper base pairing during replication. This misalignment can lead to replication errors, resulting in mutations. If these mutations occur in critical genes that regulate cell growth or repair mechanisms, they may contribute to diseases such as skin cancer, highlighting the importance of efficient DNA repair pathways.
• Discuss the role of nucleotide excision repair in addressing cyclobutane pyrimidine dimers and how it contrasts with other DNA repair mechanisms.
  • Nucleotide excision repair is essential for correcting cyclobutane pyrimidine dimers by recognizing and removing damaged sections of DNA. This process differs from other mechanisms like base excision repair, which targets smaller lesions. Nucleotide excision repair involves multiple steps: damage recognition, strand incision around the lesion, removal of the damaged segment, and synthesis of new DNA to fill the gap. This complexity allows for effective removal of bulky lesions like CPDs that could disrupt normal cellular function.
• Evaluate how exposure to UV radiation contributes to the formation of cyclobutane pyrimidine dimers and discuss potential preventive measures against such damage.
  • Exposure to UV radiation causes covalent bonding between adjacent thymine bases in DNA, resulting in cyclobutane pyrimidine dimers. To prevent this damage, individuals can take several measures such as wearing sunscreen with high SPF to block UV rays, wearing protective clothing, and seeking shade during peak sunlight hours. Additionally, awareness and education about the risks associated with excessive UV exposure can further reduce incidence rates of skin cancer linked to CPD formation.

Related terms

UV Radiation: A form of electromagnetic radiation from the sun that can cause damage to DNA, leading to the formation of cyclobutane pyrimidine dimers.

Nucleotide Excision Repair: A DNA repair mechanism that removes bulky DNA lesions, including cyclobutane pyrimidine dimers, by excising the damaged section and synthesizing new DNA.

Photoreactivation: A light-dependent repair process where specific enzymes use visible light to directly reverse the formation of cyclobutane pyrimidine dimers in DNA.