What Effect Do Ultraviolet Rays Have On Yeast Colony Growth?

twoeggfinnishBiotechnology

Dec 14, 2012 (4 years and 7 months ago)

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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 short
-
term 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 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.

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


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

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
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

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


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http://
ghr.nlm.nih.gov
/

handbook/

basics?show
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all#gene


Clancy, S. (2008). DNA Damage & Repair: Mechanisms for Maintaining DNA



Integrity. Retrieved from Nature Education database.


Deoxyribonucleic Acid (DNA)
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www.genome.gov
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25520880


DNA damage from deamination and
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[illustration]. (
n.d.
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, P. E. (2002).
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Hockberger.html


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(pp. 106
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project_ideas
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, R. J., MD. (2007, August).
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home/

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References


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, R. (2002, August 28).
What are ‘model organisms’?

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