Caroline Stroud

Ultraviolet Light and its effect on Yeast cells

November 11, 2014

Abstract: The experiment’s purpose is to show how yeast cells can be affected by UV light rays and show their relation to human skin cells. There is background information telling what yeast and skin cells have in common and why they are used for tests such as the experiment. The experiment is to determine how scientist can help prevent skin cancers and disorders that are caused by UV light ray exposure. The results showed that tanning oil did not protect the yeast cells. The results also proved that 50 SPF sunscreen is protective to the yeast cells when they are exposed to UV light. In conclusion, when humans use tanning oils they skin cells, like the yeast cells will be damaged by the UV light. When humans use 50 SPF sunscreen they are less likely to have damaged skin cells.

Background: In previous studies done by the National Institute of Health, yeast cells were used to

simulate human skin cells. Yeast cells are UV-sensitive and are a good model for testing products such as the sunscreen or tanning oils used in this experiment (NIH). The yeast’s reaction to the sensitivity to UV light is quick and the yeast is easy to grow for multiple tests (NIH). In the National Institute of Health’s experiment, the scientist tested the yeast resilience to UV light at different times of the day. The yeast was exposed to different amounts of UV rays because of the different angles of the sun. The yeast exposed in the middle of the day did not replicate as much as the yeast in the afternoon as the sun was setting. This proves that during the middle of the day there are more UV rays and that people should take precautions to limit sun exposure during this time of the day (NIH). In using this experiment and the knowledge it provides, humans can limit their unhealthy UV exposure.

In knowing that yeast cells are harmed by UV light similar to human skin cells, one is able to use the yeast cells to show how human skin cells will be affected or protected by certain UV protecting products and to test many other factors that UV light affects. The experiment conducted in class is based off the experimental design used in the National Institute of Health’s experiment.

The purpose in testing yeast cells’ acceptability to UV rays and how different products work or different times of the day affect the cells is to protect humans from the UV light rays. The rays, if human skin cells are over exposed, can damage and even mutate the cells causing two skin cancer, melanomas or carcinomas. The experiments conduct solutions and ways to prevent skin diseases and disorders.

Hypothesis: If 50 SPF sunscreen and tanning oil are put on two different plates of yeast cells before they are put under UV light, then the one with sunscreen will grow and the one with tanning oil will die.

Materials and Methods: Steps 1- 16 are for the control ager plates.

1. Put on safety goggles and gloves.

2. Obtain a wild type yeast strain starter plate and a mutant yeast strain starter plate

3. Obtain two test tubes. Label one wild type and the other mutant with a marker.

4. Get a sterile inoculation loop and collect a single colony of yeast from the starter plate labeled wild type yeast. Smear the colony in the test tube label wild type as close to the bottom as possible. Discard the loop.

5. Repeat step 4 with the mutant yeast starter plate and test tube.

6. Obtain a pipet and bottle of sterile water. Pipet 5ml of sterile water into both test tubes.

7. Shake the tubes until the yeast cells are completely immersed in the water.

8. Obtain two clean ager plates. Label one wild type yeast and the other mutant yeast.

9. Open both of the ager plates with the lid down. Put 4 – 5 glass beads onto the lid of the plates and close and flip the plates over.

10. Use the 1 mL pipet and pipet 250 μL of each yeast strain solution into its matching labeled plate.

11. Spread the yeast cells onto the plates by shaking the glass beads on the plate.

12. Discard of the glass beads when water has dried.

13. Remove the lids and cover the plates with plastic wrap.

14. Place two pieces of aluminum foil so that they cover half of the plates.

15. Place the two plates under UV light for 15 minutes.

16. Incubate the plates overnight at 30˚ C.

Steps 17-21 are for the experimental design

17. Repeat steps 1-13 using 4 plates, two of each type of yeast.

18. Using a marker label one wild type and one mutant yeast plate tanning. Label the other two, sunscreen.

19. Obtain SPF 50 sunscreen and smear it evenly on top of the plastic wrap on the two plates labeled sunscreen.

20. Obtain deep tanning oil and smear it evenly on top of the plastic wrap on the two plates labeled tanning.

21. Repeat steps 15 and 16.

Results: The control mutant type, shown below on the right, when exposed to the UV light only grew about 75%. The control wild type grew on half of the plate.

Control

Experimental Design

The tanning oil wild type and the 50 SPF sunscreen wild type both grew 100% on the plate. The tanning oil mutant type only grew 15%. The mutant type 50 SPF plate grew 100%.

Discussion: The experiment added to the information given in the background by giving people an idea of what kinds of protectant they should wear during certain times of the day. The more exposure of sun the higher the SPF level of the sunscreen should be. The error that occurred during the experiment was placing the plates on the top shelf of the UV light. This put the cells to close to the UV bulbs causing over exposure. The control plates were on top while the experiment plates were on the bottom, this resulted in error. If done again the testers should put all the plates on the same level so they are exposed to the same amounts of UV light. Another error that occurred within the experiment is the inoculation glass beads. The beads did not dry all the way and were also spun and distributed the cells along the side of the plates. Maybe if the experiment is done again a normal inoculation loop and smearing technique should be done.

An experiment that can be conducted in the future to further the knowledge of UV light and its affect on skin cells is a test on the reflection of UV light rays. There is a myth that UV light form the sun can reflect off water, sand, or another substance and still harm the skin cells. A piece of foil or tray of water could be placed under the yeast cells while exposed to UV rays, without any protective materials. The lamps would not be directly on the plates but only pointed to where they would be reflected off the substance below. This would help people be able to protect themselves from reflective materials when outside, as well as direct exposure. Conclusion: When exposed to UV light for fifteen minutes, the mutant type yeast strain that was covered with SPF sunscreen, strived while the mutant type yeast strain covered with tanning oil died.

Citation:

National Institute of Health. (1999). “Using a Model System to

Test Claims About UV Light.” Retrieved from,

https://science.education.nih.gov/supplements/nih1/cancer/guide/pdfs/ACT4M.PDF