pyrimidine dimer

chemical structure

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July 16, 2026

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A pyrimidine dimer is a type of DNA damage that occurs when adjacent pyrimidine bases, typically thymine or cytosine, fuse together. This fusion is often caused by exposure to ultraviolet (UV) radiation. The chemical structure of pyrimidines, which are nitrogen-containing heterocyclic organic compounds, makes them susceptible to this type of bonding under UV light.12

This fusion distorts the DNA double helix and can prevent DNA replication and transcription, potentially leading to mutations or cell death. Cells have repair mechanisms, such as photoreactivation, to separate these fused pyrimidines and restore the DNA's normal structure. Defects in these repair systems can increase the risk of diseases like cancer.13

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human genetic disease
Ultraviolet radiation
Such pyrimidine dimerization is mutagenic, but this damage can be repaired by an enzyme called photolyase, which utilizes the energy of longer wavelengths of light to cleave the dimers. However, people with a defect in the gene coding for photolyase develop xeroderma pigmentosum, a condition characterized…
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Such pyrimidine dimerization is mutagenic, but this damage can be repaired by an enzyme called photolyase, which utilizes the energy of longer wavelengths of light to cleave the dimers. However, people with a defect in the gene coding for photolyase develop xeroderma pigmentosum, a condition characterized…
Read More

cancer
Ultraviolet radiation
If a pyrimidine dimer in a growth regulatory gene is not immediately repaired, it can contribute to tumor development (see the section The molecular basis of cancer: DNA repair defects).
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If a pyrimidine dimer in a growth regulatory gene is not immediately repaired, it can contribute to tumor development (see the section The molecular basis of cancer: DNA repair defects).
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