1. Use of UV-sensitive yeasts at Higher and Advanced Higher
Biology Summer School 2013
Use of UV-sensitive yeasts at Higher and Advanced Higher
Kath Crawford, Lorraine Bruce

2. Aims
Explore the use of UV-sensitive yeasts to support learning and teaching of Biology and Human Biology at Higher Level

3. Unit: Metabolism and Survival
3. Metabolism in microorganisms
(b) Genetic control of metabolism
(i) Wild strains of microorganisms can be improved by mutagenesis, selective breeding and culture or recombinant DNA

4. Unit: Human Cells 2. Structure and function of DNA
(c) Genes and proteins in health and disease
(ii) Mutations result in no protein or a faulty protein being expressed

5. Unit: Investigative Biology
Scientific principles and process
Experimentation
Critical evaluation of biological research

6. Ultraviolet (UV) light
< 400 nm
More energetic than visible light
Can disrupt chemical bonds
Causes increased mutation rate in DNA

7. Wild-type yeasts (and other eukaryotic cells)
DNA routinely damaged from exposure to UV radiation in atmosphere
Protection mechanisms
enzymes repair DNA damaged by UV radiation
sometimes fail, mutations occur
Repeated exposure to UV light increases rate of damage and chance of mutations

8. UV sensitive yeasts Mutations in genes necessary for DNA repair
Deficient in DNA repair mechanisms
More sensitive than wild-type cells to sunlight

9. The activities
Expose UV-sensitive yeasts to sunlight or UV radiation for varying lengths of time (demonstration only), compare with wild-type
Carry out a simple investigation to test whether sunscreens offer protection to the damaging effects of UV irradiation

10. Results – Yeast survival vs. time ‘sunbathing’
0 min
10 min
20 min
30 min
40 min

12. Using aseptic technique, pick off a small, isolated colony from the master plate of
UV-sensitive Saccharomyces cerevisiae and add to 10 cm3 sterile Ringer’s solution. Mix well.
Using aseptic technique, carry out a x10 serial dilution to achieve a final dilution of 10-3

15. The serial dilution

16. Disposable pipettes 100 µl onto plates

17. Use sterile loop to spread evenly across plate, Sellotape closed
Aseptically, pipette 100 µl 10-3 dilution onto each of 5 labelled YGA plates
Use sterile loop to spread evenly across plate, Sellotape closed
Aluminium foil
No cover
E45
Factor 6
Factor 30
Irradiate with UV for 1 hour (sunlight or UV lamp)
Incubate 30°C for 48 hours

18. Effect of different strengths of sunscreen on UV irradiation of UV-sensitive yeast
No irradiation
SPF O
SPF 6
SPF 15
SPF 25

19. From melanocyte to melanoma
Use of yeast as a model organism
Implication of exposure to UV irradiation as a cause of skin cancer
From melanocyte to melanoma

20. http://www. cancerresearchuk

21. Malignant melanoma is the fastest increasing cancer in males and the second fastest increasing cancer in females
Some of the increase may be due to increased surveillance and early detection as well as improved diagnosis
most is considered to be real and linked to changes in recreational or holiday exposure to UV rays (including sunlight and sunbeds)

24. http://www. metoffice. gov. uk/public/weather/forecast/#

25. http://www. isdscotland

27. Health Warning
Sunbed use may damage your skin and will increase your risk of skin cancer!

28. What would we want the students to learn?
Knowledge and understanding
UV-irradiation causes mutations in DNA
Improvement to wild-type
Changes in protein expression
Yeast as a model organism
Relevance to understanding of skin cancer
Techniques
Serial dilution
Microbiology

29. Skills of scientific experimentation, investigation and enquiry
Planning and designing
Experimental design to ensure validity of procedures
Evaluating experimental procedures
Identify and comment on validity of experimental designs
Drawing conclusions
Draw conclusions on the relationships between the dependent and independent variables

31. Irradiation with sunlight
Group
Total
Average
% of average number of colonies at SPF30 1 2 3 4 5
No irradiation 12 8 9 35 7
54%
Full irradiation 0%
E45 15 14 44
69%
SPF10 10 13 25 60
92%
SPF30 6 22 66
100%

32. Irradiation with UV lamp ( 365 nm)
Group
Total
Average
% of average number of colonies at SPF30 1 2 3 4
No irradiation 20 12 32 66 17
53%
Full irradiation 9 21 5
16%
E45 40 45 11
34%
SPF10 25 6 82
66%
SPF30 14
100 10
128
100%

33. % of average number of colonies found at SPF30
Sunlight
UV lamp (365 nm)
54%
53% 0%
16%
69%
34%
92%
66%
100%