Pyrimidine dimer

Pyrimidine dimers are molecular lesions formed from thymine or cytosine bases in DNA via photochemical reactions. Ultraviolet light (UV) induces the formation of covalent linkages by reactions localized on a single strand of DNA, generating cyclobutane pyrimidine dimers (CPDs) and 6-4 photoproducts. These are considered the principal DNA lesions caused by UV light.

Formation

Pyrimidine dimers are formed by a photochemical reaction from thymine or cytosine bases in DNA. This reaction is caused by exposure to ultraviolet (UV) light. The absorption of UV light by the DNA molecule leads to the formation of covalent linkages between consecutive bases along the nucleotide chain. This process is known as dimerization.

Types

There are two types of pyrimidine dimers: cyclobutane pyrimidine dimers (CPDs) and 6-4 photoproducts. CPDs are the most common type of lesion caused by UV light. They are formed between two adjacent pyrimidines on the same DNA strand. 6-4 photoproducts are less common, but they are more detrimental to the cell because they distort the DNA helix significantly more than CPDs.

Effects

Pyrimidine dimers interfere with normal cellular processes such as DNA replication and transcription. This can lead to mutations and cell death. In humans, these mutations can lead to skin cancer, including melanoma and non-melanoma skin cancer.

Repair

Cells have mechanisms to repair pyrimidine dimers. The most common repair mechanism is nucleotide excision repair (NER), which removes the damaged section of DNA and replaces it with correct nucleotides. Another mechanism is photoreactivation, which uses light energy to reverse the dimerization reaction.

See also

• DNA repair
• Nucleotide excision repair
• Photoreactivation

Pyrimidine dimer Resources
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