What Effect Do Ultraviolet Rays
Have On Yeast Colony Growth?
By Katie Schneider
Grade 10
Academy of Notre Dame de Namur
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 shortterm sign of UV damage, but skin aging and
skin cancer are long-term effects of UV
damage.
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.
Research
• In this experiment, the Saccharomyces
cerivisiae is genetically engineered to be DNArepair-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.
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.
Materials
•
•
•
•
•
•
•
•
UV-sensitive yeast strain
Sterile dilution tubes
Sterile toothpicks
Dextrose (YED)
Petri dishes
Sterile distilled water
Pipettes
Glass spreading beads
Materials
•
•
•
•
•
•
•
•
Disposable gloves
Microwave oven
Permanent marker
Aluminum foil
Stopwatch
Cardboard box
3 UV flashlights
Transparent sticker with 34 sections
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
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
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,
Data
Number of Sections Showing Yeast Growth out of 34
Trial #
Control
1 min
Exposed Control
1 min
3 min
Exposed Control
3 min
5 min
Exposed Control
5 min
7 min
Exposed
7 min
1
34
34
18
30
34
0
34
34
2
32
30
34
0
26
33
34
0
3
0
34
34
34
34
34
34
34
Average
22
33
29
21
31
22
34
23
Data
Average Yeast Growth
45
40
Number of Sections with growth out of 34
35
30
25
20
15
10
5
0
control 1 min
exposed 1 min
control 3 min
exposed 3 min
control 5 min
Amount of time exposed to UV light
exposed 5 min
control 7 min
exposed 7 min
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.
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-fairprojects/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
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-israelwatertreatment&SingleRecord=True
Ultraviolet (UV) Radiation. (2010, August 17). Retrieved from http://www.fda.gov/RadiationEmittingProducts/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