Name: Sarah
Status: Student
Grade: 9-12
Location: N/A
Country: United States
Date: October 2008
Question:
How does UV Radiation physically affect bacteria?
Replies:
UV causes adjacent thymine molecules to react with each other to form TT
dimers. These dimers prevent DNA replication. DNA repair enzyme can excise
them but mistakes are made during this repair which produces mutations.
Ron Baker, Ph.D.
UV radiation generally carries out its biological effect by damaging nucleic
acids. The chromophores in sugars and proteins do not generally absorb in
wavelengths of UV that reach the Earth's surface, so those biomolecules are
not UV-sensitive. The purine and pyrimidine bases in nucleic acids, on the
other hand, do absorb UV. The added energy excites them to a higher electronic
state. In particular, thymidine, the nucleobase in thymine, can dimerize when
exposed to UV. This causes defects in transcription and replication.
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