1 Experiment 2-13: The Lethal Effect of Ultraviolet Light on Microbial Growth (pgs. 55-57) Purpose : To determine the effect of Ultraviolet (UV) light on bacterial growth. Ultraviolet (UV) light: A. A type of electromagetic energy B. Travels in waves and is distinguishable by its wavelength ranging from 1nm to 400nm (or 1Å to 400Å) C. Divided into three groups: 1. UV-A: longest wavelength from 315 to 400 nm 2. UV-B: wavelength between 280 to 315 nm 3. UV-C: wavelength from 100 to 280 nm (most detrimental to bacteria) 260 nm = wavelength that DNA and RNA concentration is determined 280 nm = wavelength that protein concentration is determined 265 nm = wavelength that is most damaging to DNA (wavelength emitted by our UV lamps) Prolonged exposure to UV light usually causes death of a bacterial organism by causing DNA damage in the form of pyrimidine dimers (thymine dimers are the most common) that cannot be repaired by the organism’s DNA repair mechanisms. 1
This is the end of the preview. Sign up
access the rest of the document.