University:
Boston University
Course:
CAS PY 521 | Electromagnetic Theory I
Academic year:

2022
Views:

375

Pages:

7
Author:

paproszekmca5

UV light: Lethal Effects • Plate out bacteria – Sterile swab – Cover entire plate!!! • Take off lid • Place note card over half of plate – Label side exposed to UV • Place plate under hood for different amounts of time UV light: Lethal Effects • • • • • Break up into 4 groups Group 1: S. epidermis 10sec, 20 sec, 40sec, 80 sec Group 2: S. epidermis 2.5 min, 5 min, 10 min 10min* Group 3: B. megaterium 1min, 2min, 4 min, 8 min Group 4: B. megaterium 15 min, 30 min, 60 min 60 min* • 8 plates/group: repeat experiment twice • * = leave lid on UV light • Ultraviolet light: short wavelength radiation falls between 4nm and 400nm • Electromagnetic radiation: shorter the wavelength more harmful it is to cells UV light: Lethal effects • 260nm • UV light is absorbed by DNA • Pyrimidine dimers – – – – Covalent bond Adjacent Cytosine C=C Thymine T=T • Prevents • Replication (copying DNA) • Transcription (DNAmRNA) need this to happen to make protein UV Light Lethal effects experiment • UV light • Time of exposure • Blocking materials – Note card – Plastic • Properties of bacteria – Spore former vs. non spore former UV Light Results Look at plates 1) Quantify Growth on side of plate that was exposed to UV light 1) +++ substantial growth 2) ++ moderate survival 3) + 3 or fewer colonies 4) - no growth 2) Fill out chart 3) Report results so they can be shared with the class Organism S. epidermis Exposur e Time 10 sec 20 sec 40 sec 80 sec 2.5 min 5 min 10 min 10min * 1 min 2 min 4 min 8 min 15 min 30 min 60 min 60min * Survival B. Megaterium Survival Example Data Set Organism Exposure Time S. epidermis 10 sec 20 sec 40 sec 80 sec 2.5 min 5 min 10 min 10min * Survival +++ ++ ++ + + - - B. Megaterium 1 min 2 min 4 min 8 min 15 min 30 min 60 min 60min * Survival +++ ++ ++ + - - - +++ +++