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14 Δεκ 2012 (πριν από 4 χρόνια και 10 μήνες)

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What Effect Do
Ultraviolet Rays Have
On Yeast Colony
Growth?

By Katie Schneider

Grade 10

Research


UV
-
A
light causes
tanning, skin aging, and
cataracts


UV
-
B causes sunburn, skin aging and skin
cancer


UV
-
C is
most
effective at killing
microorganisms

Research


UVA radiation
causes
2 types of DNA
damage:


cyclobutane

pyrimidine
dimers


6
-
4
photoproducts


These
2 types of damage are repaired by nucleotide excision
repair

Research


In this experiment, the
Saccharomyces
cerivisiae

is genetically
engineered to be DNA
-
repair
-
deficient


The
enzymes that normally would repair DNA damage are
knocked out so that the yeast is especially sensitive to UV
light

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 purchased from
Carolina Biological


Sterile dilution tubes


Sterile toothpicks


Dextrose (YED)


Petri dishes


Sterile distilled water


Pipettes


Glass spreading beads


Disposable
gloves


Microwave oven


Permanent marker


Aluminum foil


Stopwatch


Cardboard box


3 UV flashlights


Transparent sticker
with 34 sections


Procedure


T
he
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


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

Procedure


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, size of the
petri

dishes


Photos

Data

Number

of Sections Showing Yeast Growth out of 34

Trial #

Control
1 min

Exposed
1 min

Control
3 min

Exposed
3 min

Control

5 min

Exposed
5 min

Control
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

0
5
10
15
20
25
30
35
40
45
control 1 min
exposed 1 min
control 3 min
exposed 3 min
control 5 min
exposed 5 min
control 7 min
exposed 7 min
Number of Sections with growth out of 34

Amount of time exposed to UV light

Average Yeast Growth

Sources of Error and
Improvements


This project
should be conducted in the summer so that sunlight can
be used as UV light instead of UV
flashlights.


Also
, in this experiment, the data was measured by determining
whether there was growth in each of 34 different
sections.
Any
growth at all in a designated grid section was considered a positive
result.


Also
, when spreading the yeast suspension with the glass beads, it
ended up being concentrated primarily around the perimeter of the
dishes, so this may have affected the results.



If
this experiment were to be performed again, one should use a
higher serial dilution level, such as 1:1000 instead of 1:100, and an
alternate method for counting the yeast growth should be used that
yields more accurate results.


Additional
trials performed using these changes might result in data
that is more reliable
.

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


Because
of the high standard deviation,
however, the
results
may not be reliable.


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.



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


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




References