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

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

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

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

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

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

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

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

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

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

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

The serial dilution

Disposable pipettes 100 µl onto plates

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

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

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

http://www. cancerresearchuk http://www.cancerresearchuk.org/cancer-info/cancerstats/incidence/commoncancers/#Twenty

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)

http://www. metoffice. gov. uk/public/weather/forecast/# http://www.metoffice.gov.uk/public/weather/forecast/#?tab=map&fcTime=1371427200&map=MaxUVIndex&zoom=5&lon=-4.00&lat=54.63

http://www. isdscotland http://www.isdscotland.org/Health-Topics/Cancer/Publications/2012-10-30/Cancer_in_Scotland_summary_m.pdf

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

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

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

Kath.Crawford@sserc.org.uk Lorraine.Bruce@sserc.org.uk

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%

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%

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