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Thymine dimer

Written by the Fiveable Content Team • Last updated August 2025
Written by the Fiveable Content Team • Last updated August 2025

Definition

A thymine dimer is a type of DNA damage caused by ultraviolet (UV) radiation in which two adjacent thymine bases bond together, disrupting normal DNA structure. This can lead to mutations if not repaired.

AP course connection

Topic 13.2: 13.2 Using Physical Methods to Control Microorganisms

Unit 13

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5 Must Know Facts For Your Next Test

  1. Thymine dimers are primarily induced by UVB light from the sun.
  2. They cause a kink or distortion in the DNA helix, which can interfere with replication and transcription processes.
  3. If unrepaired, thymine dimers can result in mutations that may lead to skin cancers like melanoma.
  4. Cells repair thymine dimers through nucleotide excision repair (NER) mechanisms.
  5. Thymine dimer formation is one reason why sunscreens are important for protecting skin from UV damage.
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