1. Introduction

1.1 Background research 

The purpose of our study is to find out the lethal DNA effects of sunlight on UV-sensitive yeast. Most living things have already, through evolution and adaptation, have managed to reverse or repair radiation damage so as to continue life despite UV radiation. Photoreactivation is one of the most efficient repair systems. When UV-damaged cells are exposed to sunlight that has the UV wavelengths filtered out, a specific enzyme in the cell uses the energy from the visible part of the solar spectrum to reverse the reaction that produces pyrimidine dimers. If the dimers are repaired before the DNA tries to replicate them, they have no effect on the cell. Humans have fewer types of repair mechanisms. In all organisms mutations often occur during less accurate repair processes, accounting for the mutagenic action of UV radiation. In cells the survivors of radiation exposure may be affected. There are many long-term effects in multicellular organisms, the most significant being the increased risk of cancer. (The Response of Yeast to Radiation, 1997) UV light does slowly penetrate and destroy the cell membranes of yeast. UV radiation does not kill yeast cells straightaway, but damages their DNA. It occurs when the order in DNA is altered, which causes its characteristics change too. Low intensity UV rays will affect a yeast population by causing them to mutate.  When yeast cells are exposed to higher UV radiation, their DNA becomes irreparably damaged by the UV radiation. If half of a yeast colony is killed by UV radiation, the other half may grow rapidly. (The Effects of Ultraviolet Radiation on Yeast, 2010) According to Future Science Leaders (n.d.), these are the reasons why yeast cells are often used in research. Yeasts are microorganisms which are unicellular and eukaryotic like human cells. Yeast are safe to work with, and they do not need any special handling. They are safer compared to bacteria and some other organisms. Yeasts are also simpler organisms compared to humans, because they do not have complex organs and body systems. Because of yeasts’ similarity to human cells together with their simplicity, makes them easy to be used in experiments. Furthermore, yeast genes are also quite similar to human genes, allowing researches to do trials on yeast that can be related to humans. This saves time, money and energy. Because of the overlapping genes in yeasts and humans, yeasts are a excellent models to experiment with. For example, yeast genes can be removed and replaced with human genes to test drugs and mutagens. These similarities have helped with advances and improvements in the research field.



1.2 Research Questions

  1. What negative effects do UV rays have on UV-sensitive yeast?
  2. Why is yeast used in experiments?
  3. How do yeast cells respond to UV radiation?
  4. How are yeast and human cells similar?  
  5. What is photoreaction?


1.3 Hypothesis

If UV-sensitive yeast is exposed to UV rays, then there would be lethal DNA effects on the yeast, causing the yeast to be unable to function properly.


1.3.1 Independent Variables

  1. Intensity of UV rays


1.3.2 Dependent Variables

  1. DNA Change in UV sensitive yeast cells


1.3.3 Constants

  1. Yeast cells strains
  2. Type of UV rays used (UVA/UVB)
  3. Time the yeast cells are exposed to UV rays
  4. Number of yeast cells

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