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UV-sensitive Yeasts in Biology Education: Impact of UV Irradiation on DNA Repair Mechanisms

Explore the educational use of UV-sensitive yeasts to study DNA repair mechanisms in Biology and Human Biology. Learn about UV light effects on DNA, mutations, and the potential impact on skin cancer development. Conduct experiments to compare UV-sensitive yeasts with wild-type cells under different conditions. Gain insights into relevant scientific principles and critical evaluation of biological research.

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UV-sensitive Yeasts in Biology Education: Impact of UV Irradiation on DNA Repair Mechanisms

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  1. 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’ 10 min 20 min 0 min 40 min 30 min

  11. 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

  12. The serial dilution

  13. Disposable pipettes100 µl onto plates

  14. 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

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

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

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

  18. 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)

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

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

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

  22. 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

  23. 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

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

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