Presentation on theme: "What Effect Do Ultraviolet Rays Have On Yeast Colony Growth? By Katie Schneider Grade 10 Academy of Notre Dame de Namur."— Presentation transcript:
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.
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 1 min Control 3 min Exposed 3 min Control 5 min Exposed 5 min Control 7 min Exposed 7 min Average
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.
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