Chylee Martin, Helaina Lefler

Activity 3.2.2 Skin Cancer

November 5th, 2014

Abstract: The experiment’s purpose is to determine the effects of UV rays on wild type and mutant yeast when exposed directly, or covered with SPF 30 or tanning oil in order to find the best ways to protect skin from UV rays. The wild type and mutant yeast cells were spread on individual agar plates, covered with tin foil, SPF 30, tanning oil, or nothing at all and exposed to UV rays in a light box. Since wild type grows regardless of UV exposure, it was the control; mutant yeast dies when exposed to UV rays, so it was used to represent skin cells. The results concluded that SPF 30 protects the mutant yeast better than tanning oil.

Background:

Caitlin R. Russell did an experiment in 2006 to determine the effect of UV rays on normal and G948-1C/U yeast cells. She covered individual plates of yeast in foil, cotton fabric, and sunscreen (SPF 15 and SPF 30) and one was left exposed to sun rays. Over the course of 100 minutes the plates were observed. She concluded that the wild type yeast strain did not appear to be greatly affected by UV rays. The UV sensitive G948-1C/U strain had little or no growth.

Hypothesis: The sunscreen with a higher SPF will better protect the mutant yeast cells from the UV rays than the tanning oil.

Materials:

Safety goggles Latex or nitrile exam gloves Carolina’s Sunscreen for Yeast and People, Too lab kit YED plates Bottle of sterile water Sterile, capped, plastic test tubes 1 mL individually wrapped sterile bulb pipets 5 mL individually wrapped sterile bulb pipets Small jar of glass beads Box of sterile toothpicks Starter plate with UV light-sensitive yeast strain (mutant yeast strain) Starter plate with wild-type yeast strain Aluminum foil squares (approx., 12 cm x 12 cm) Stop watch 30 ˚C Incubator Various types of sunscreens or tanning oils

Methods:

Obtain two clean separate plastic tubes, and label them as WT (for the wild yeast strain) and MT (for mutant yeast strain). Collect two separate samples of the wild yeast strain and the mutant yeast strain, and place them at the bottom of their respective tubes and label each tube either WT or MT. Load 5mL of sterile water into each tube, and shake the tubes to mix the water with the yeast until the water appears cloudy. Then, pipet 1mL of each solution into their tubes onto two WT and MT labeled YED plates (at least three plates per type). Shake 4 to 5 glass beads onto the

plate and, with the lid on, shake the beads around each plate to evenly distribute the yeast samples. Wait and let the yeast soak into the agar. Label each plate with the yeast type. On one WT and one MT plate, cover half of the plate with tin foil and label which side is exposed to UV and which side is not. Put these two plates on the middle rack of the UV light box. After UV exposure, incubate the plates at 30˚ C overnight. Use these as the control. Take the lids off the rest of the agar plates and cover each plate with plastic wrap. Cover the plastic wrap of one WT and one MT plate with SPF 30 and the plastic wrap of the last WT and MT plates with tanning oil. Repeat the UV light box and incubation process.

Results:

The control wild type grew on 30% of the plate that was not exposed to the UV rays. The other side that was exposed to the sun did not grow any yeast. The control mutant yeast grew on both sides, approximately 20% of the plate. The WT that was manipulated by covering the plate with tanning oil did not grow at all. The MT did not grow on the plate that was covered with tanning oil. The WT that was covered with SPF 30 grew on 100% of the plate. The MT that was covered with SPF 30 grew on approximately 50% of the plate.

Table 1

Growth Results (%)Sun No Sun Tanning Oil SPF 30

Wild Type 0 33 0 100Mutant Type 20 20 0 50

Discussion:

The WT yeast should have grown all over the plate that was half exposed to UV rays because the WT yeast has not mutated and does not die when exposed to UV rays. The plate was placed on the top shelf closest to the UV rays in the light box, so the heat from the lamp could have killed the yeast because it was so close. The MT yeast grew on 20% and both sides of the plate regardless of the fact that one side was fully exposed to UV rays that should have killed the yeast. The WT yeast plate that was covered in SPF 30 grew on 100% of the plate because SPF protects against UV rays. The WT yeast that was covered with tanning oil and exposed to UV rays did not grow at all even though WT does not die when exposed to UV rays; the plate could have been too close to the UV lamp in the light box and the heat may have killed the yeast. To avoid the UV lamp killing the yeast cells, place the plates on the middle or lower shelves of the light box. The MT yeast that was covered with SPF 30 grew on 50% of the plate, which was expected because MT yeast dies when exposed to UV rays and the SPF 30 protects against them.

The MT yeast did not grow on the plate that was covered with tanning oil and exposed to UV rays because MT dies when exposed to UV rays and tanning oil amplifies the UV rays.

Conclusion:

The SPF 30 sunscreen better protected the mutant type yeast from UV rays than the tanning oil and allowed the yeast to grow.

Citations:

Russell, Caitlin R. "EFFECTS OF ULTRAVIOLET RADIATION ON YEAST."Angelfire. N.p.,

6 Dec. 2006. Web. 11 Nov. 2014.