What Effect Do Ultraviolet Rays Have On Yeast Colony Growth?

1. What Effect Do Ultraviolet Rays Have On Yeast Colony Growth? By Katie Schneider Grade 10 Academy of Notre Dame de Namur

2. Research • UV-A light, specifically, is what mainly causes tanning, skin aging, and cataracts, UV-B causes sunburn, skin aging and skin cancer, and UV-C is the strongest, and therefore most effective at killing microorganisms. Sunburn is a short-term sign of UV damage, but skin aging and skin cancer are long-term effects of UV damage.

3. Research • UVA radiation specifically causes 2 types of DNA damage: cyclobutane pyrimidine dimers and 6-4 photoproducts, both of which cause bends in DNA structure, therefore hindering replication and transcription. These 2 types of damage are repaired by nucleotide excision repair, in which the damage is detected, the section of DNA that includes the damage is removed, and it is filled in with new DNA by DNA polymerase.

4. Research • In this experiment, the Saccharomyces cerivisiae is genetically engineered to be DNA-repair-deficient. This means that the enzymes that normally would repair DNA damage are knocked out so that the yeast is especially sensitive to UV light. This helps to show what effect that gene has in yeast’s lives, and how fatal UV light would be if the DNA damage was not repaired.

5. Hypothesis • If yeast colonies are exposed to UV light for varied amounts of time, a short amount of UV exposure will aid in yeast production, but longer exposure will kill the yeast cells because of the damaging effects of UV light.

6. Materials • UV-sensitive yeast strain • Sterile dilution tubes • Sterile toothpicks • Dextrose (YED) • Petri dishes • Sterile distilled water • Pipettes • Glass spreading beads

7. Materials • Disposable gloves • Microwave oven • Permanent marker • Aluminum foil • Stopwatch • Cardboard box • 3 UV flashlights • Transparent sticker with 34 sections

8. Procedure • The agar plates were poured by heating sterile YED agar in a microwave then pouring the agar onto 25 petri dishes • The master plate was then streaked with yeast • To determine the optimal serial dilution needed for the experiment, 1:1,000 and 1:10,000 dilutions of a yeast suspension made from the growth on the master plate were tested • They showed no growth, so they were tested again, but without UV exposure • They again showed no growth, so 1:10 and 1:100 dilutions were tested • The 1:10 dilution provided growth that was too dense, so 1:100 dilution was used for actual experimentation • Plastic test tubes and sterile bulb pipettes were then used to make the 1:100 serial dilution of the yeast suspension

9. Procedure • 2.5 mL of this suspension was pipetted into each petri dish, which was labeled either exposed or control for 1, 3, 5, or 7 minutes, with 3 trials for each • 5 glass beads were placed in each petri dish, which were swirled across the plate to spread the yeast suspension • Three holes were made across the middle of a cardboard box, and UV flashlights emitting light in the 385 nm range were places in the openings • Three petri dishes at a time were then exposed to the light for their indicated times • Controls were covered in aluminum foil before being exposed to the UV light • The exposed samples were then covered in aluminum foil, and stored in an incubator for 2 days at 30°C

10. Procedure • To collect the data, a transparent grid containing 34 sections was placed over the petri dish • The number of sections containing yeast growth out of 34 was then recorded • There were 3 trials for each amount of time for control and exposed • Independent variable-the amount of time the yeast was exposed to UV light • Dependent variable-the amount of yeast growth • Control-the yeast not exposed to UV light • Constants-amount of yeast in each petri dish, sixe of the petri dishes,

11. Data

12. Data

13. Conclusion • Hypothesis-“a short amount of time will aid in yeast production, but a longer amount of time will kill the yeast cells because of the damaging effects of UV light.” • The results support the hypothesis, however, because of the high standard deviation, the results were proven to be unreliable. • This experiment has relevance to the world today because UV light is a major cause of skin cancer, and extended exposure can be extremely detrimental to skin health. • Other experiments regarding UV light could be conducted testing the strength of UV at different times of day, during different seasons, or for longer periods of time.

14. References • Cells and DNA. (2011, October 17). Retrieved from http://ghr.nlm.nih.gov/‌handbook/‌basics?show=all#gene • Clancy, S. (2008). DNA Damage & Repair: Mechanisms for Maintaining DNA • Integrity. Retrieved from Nature Education database. • Deoxyribonucleic Acid (DNA). (2011, March 23). Retrieved from http://www.genome.gov/‌25520880 • DNA damage from deamination and depurination [illustration]. (n.d.). Retrieved from Science Online database. • Genetic Engineering. (2011, May 23). Retrieved from http://www.fda.gov/‌AnimalVeterinary/‌DevelopmentApprovalProcess/‌GeneticEngineering/‌default.htm • Goodman, B., MA. (2011, October 6). UVA Radiation May Cause DNA Damage in Skin. Retrieved from http://www.webmd.com/‌healthy-beauty/‌news/‌20111006/‌uva-radiation-may-cause-dna-damage-in-skin • Highland, J. (n.d.). The Effects of UV Light on Yeast. Retrieved from http://www.livestrong.com/‌article/‌252729-the-effects-of-uv-light-on-yeast/ • Hockberger, P. E. (2002). History of Ultraviolet Photobiology. Retrieved from Department of Physiology, Feinberg School of Medicine, Northwestern University website: http://www.photobiology.info/‌Hockberger.html • Kirkland, K., PhD. (2007). Infrared and Ultraviolet. In Light and Optics (pp. 106-109). New York: Facts On File, Inc. • Liu, S., & Usinger, L. (n.d.). All About Agar. Retrieved from http://www.sciencebuddies.org/‌science-fair-projects/‌project_ideas/‌MicroBio_Agar.shtml • MacNeal, R. J., MD. (2007, August). Overview of Sunlight and Skin Damage. Retrieved from Merck website: http://www.merckmanuals.com/‌home/‌skin_disorders/‌sunlight_and_skin_damage/‌overview_of_sunlight_and_skin_damage.html

15. References • Maczulak, A. (n.d.). Saccharomyces. In Encyclopedia of Microbiology. Retrieved from http://www.fofweb.com/‌activelink2.asp?ItemID=WE40&SID=5&iPin=EMBIO0159&SingleRecord=True • Tanner, F. W., & Ryder, E. (1923, May). Action of Ultraviolet Light on Yeast-Like Fungi. Botanical Gazette, 75(3), 309. Retrieved from http://www.jstor.org/‌pss/‌2470221 • Twyman, R. (2002, August 28). What are ‘model organisms’? Retrieved from http://genome.wellcome.ac.uk/‌doc_wtd020803.html • Ultraviolet radiation and human health. (2009, December). Retrieved from World Health Organization database. • Ultraviolet treatment for water suggested. (2010). Biofouling. Retrieved from http://www.fofweb.com/‌activelink2.asp?ItemID=WE40&SID=5&iPin=UPI-1-20100422-140951-bc-israel-watertreatment&SingleRecord=True • Ultraviolet (UV) Radiation. (2010, August 17). Retrieved from http://www.fda.gov/‌Radiation-EmittingProducts/‌RadiationEmittingProductsandProcedures/‌Tanning/‌ucm116425.htm • Whyte, D. B. (2009, December 4). Exploring DNA Damage: What Effect Do Ultraviolet Rays Have on Yeast Colony Growth? . • Wyman, B., & Stevenson, H. L. (n.d.). Ultraviolet radiation–A range (UV-A). In The Facts On File Dictionary of Environmental Science, Third Edition. Retrieved from http://www.fofweb.com/‌activelink2.asp?ItemID=WE40&SID=5&iPin=DEST4675&SingleRecord=True • Wyman, B., & Stevenson, H. L. (n.d.). Ultraviolet radiation–B range (UV-B). In The Facts On File Dictionary of Environmental Science, Third Edition. Retrieved from http://www.fofweb.com/‌activelink2.asp?ItemID=WE40&SID=5&iPin=DEST4676&SingleRecord=True • Wyman, B., & Stevenson, H. L. (n.d.). Ultraviolet radiation–C range (UV-C). In The Facts On File Dictionary of Environmental Science, Third Edition. Retrieved from http://www.fofweb.com/‌activelink2.asp?ItemID=WE40&SID=5&iPin=DEST4677&SingleRecord=True