MCB 3020L Chapter Notes - Chapter 17: Pyrimidine Dimer, Non-Ionizing Radiation, Thymine
Document Summary
Chapter 17: effects of ultraviolet light on bacteria. Uv radiation: part of the non-ionizing radiation spectrum: divided into three types- according to wavelength and biological effects. Uv-a: wavelengths of 320-400 nm: compromises ~95% of solar radiation. Indirectly induces dna damage by the activation of certain proteins (photosensitizers: uv-a is poorly absorbed by the dna molecules- forms little or no dna photoaducts. Uv-b: 290-320 nm: directly absorbed by nucleic acids (such as dna and rna) to form pyrimidine dimers. These dimers are almost always thymine dimers- two adjacent thymine molecules that become covalently crosslinked on the same dna strand, which in turn distorts the configuration of the particular dna strand in question. Distortion caused by these dimers in the genomic dna causes the dna polymerase to stall and dissociate, which in turn can lead to regions of single-stranded dna. **unless it is repaired, this dimerization can act as a lethal event for the cell in question.
