How does UVC light Kill bacteria?

UV rays are classified into three ranges depending on their wavelengths. Each range can penetrate human skin at various extents. UV-A (320nm-400nm) consists of 95% of naturally available UV radiation on earth. It can penetrate deep into human skin, which results in delayed tanning and premature aging. UV-B (280nm -320nm) penetrates the upper layer of skin and is the leading cause of skin cancer. An extended exposure can lead to skin cancer.

UV-C (100-280nm) light has germicidal properties and can even neutralize superbugs that have developed resistance to antibiotics. It does so by destroying the molecular bonds which hold their DNA. Scrambling it rendering it unable to perform cell functions, including reproduction.

All microorganisms contain either DNA or RNA. DNA is made up of nucleotides. Every nucleotide has a phosphate group, sugar group, and a nitrogen base. Adenine (A), Thymine (T), Guanine (G), Cytosine(C) are the four nitrogen bases. The order of their bases is essential in determining the DNA’s an instruction/ genetic code. RNA also contains an unmethylated form of thymine known as Uracil.  

UV kills cells because of the accumulation of DNA damage. The UV light initiates a reaction between two thymine molecules resulting in a stable thymine dimer, thus damaging the DNA. A gene called p53 is responsible for slowing down the cell cycle, and damage checks get activated. If the damage is fixable, this gene initiates repair by removing these two thymine molecules and filling the gaps with new nucleotides. If the damage is too extensive, the gene p53 directs the cell to apoptosis or programmed cell death.

 Prolonged exposure to UV rays ensures more thymine dimers are formed and increases the risk of incorrect repair or permanent damage rendering the cell unable to carry out normal functions. UV-C light is a non-chemical disinfection approach. It is inexpensive, easy to use, and has low lifetime maintenance. Most of UV-C purifiers utilize germicidal designed to produce a specific dosage of UV light.

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