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#UV radiation

2 public questions tagged with this topic.

Mutation and Mutagenesis

UV radiation mainly causes formation of

Ultraviolet radiation at 254-280 nm causes adjacent pyrimidines on same strand to undergo photochemical cyclization forming cyclobutane pyrimidine dimers and 6-4 photoproducts, covalently linking C5-C6 double bonds and distorting double helix by kinking backbone about 30 degrees. Thymine-thymine dimers are most frequent due to sequence abundance, blocking transcription and replication leading to mutations if translesion polymerases bypass incorrectly. Nucleotide excision repair employs UvrABC in bacteria and XPC-Rad23 in humans to excise damaged oligonucleotide segment. This principle illustrates essential molecular mechanisms governing replication fidelity and mutation fixation relevant for exam interpretation.

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 5: UV-Induced Pyrimidine Dimer Formation

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UV-VIS spectroscopy

What defines Vacuum UV?

Vacuum UV refers to wavelengths so energetic that atmospheric oxygen, nitrogen and water vapor absorb strongly, necessitating evacuated optical paths and special detectors. It generally spans below approximately 190 nm down to about 10 nm, where σ→σ* transitions of single bonds and high-energy n→σ* transitions occur with very high molar absorptivity. Standard glass and quartz cuvettes as well as air-filled spectrometers cannot transmit in this region. Fluoride optics, synchrotron sources and purged chambers are required. Biological macromolecules show intense peptide absorption here, but routine assays avoid vacuum UV due to technical constraints, using near UV instead.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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