How UV cause DNA damage

Thymine dimer formation, a common consequence of UV light exposure to DNA, leads to several significant biological effects: Disruption of DNA Replication: Thymine dimers create obstacles for DNA polymerase, the enzyme responsible for copying DNA. This can lead to replication stalling or errors, potentially causing mutations if not correctly repaired. Interference with Transcription: Similarly, thymine dimers can obstruct RNA polymerase during transcription, preventing the proper synthesis of RNA from the DNA template. This can disrupt gene expression and protein production. Mutagenesis: If not repaired accurately, thymine dimers can lead to permanent mutations in the DNA sequence. These mutations can result in incorrect protein synthesis or the loss of protein function, contributing to diseases like cancer. Cellular Responses and DNA Repair Activation: The presence of thymine dimers triggers several cellular responses, including the activation of DNA repair mechanisms like nucleotide excision repair (NER). If repair is unsuccessful, it may lead to cell cycle arrest, apoptosis (programmed cell death), or senescence to prevent the propagation of damaged DNA. Increased Risk of Skin Cancer: In humans, prolonged UV exposure and resultant thymine dimers significantly increase the risk of skin cancers, such as melanoma, basal cell carcinoma, and squamous cell carcinoma. This is particularly evident in individuals with genetic conditions that impair DNA repair mechanisms, such as xeroderma pigmentosum (XP). Thymine dimers are a critical form of DNA damage that underscores the importance of effective DNA repair mechanisms in maintaining genomic integrity and preventing disease.