Mutagenic Effects of Uv Light

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University Of Botswana

BIO111: Laboratory Exercise 8
The Mutagenic Effects of UV Light
Name: sharon reakae

A mutation is a permanent change in the DNA sequence of a gene. Mutation rates are usually very low but there are factors that can increase the mutation rates. These factors are referred to as mutagens and conclude a range of physic-chemical agents. UV light is a mutagen that affects all living things and has an adverse effect on the replication process of DNA within cells(.Leonard,2002) In this experiment we examine the effects of UV light on the growth of different bacteria. Cells are exposed to this radiation for different time intervals to also examine the sensitivity of each cell to each light. The exercise answers questions as to why he lid on the petri dish was removed during exposure time an analyse whether the cells test were equally sensitive to UV light and we also explore the relationship UV has with the time of exposure. The bacteria exposed to UV light for longer would either multiply very insignificantly or not multiply at all and also the different bacteria species have different sensitivity levels to this kind of radiation. We can conclude or draw a hypothesis that UV light is a mutagen that inhibits the DNA replication process that gives rise to cell division thus cell growth or multiplication. According to Keary,P.S.(1994) a genome increases the frequency of mutations above the natural background level. Not all mutations are caused by mutagens. Electromagnetic waves shorter than visible light, including UV, gamma rays and x-rays are mutagenic. Ultraviolet, x-ray and gamma –radiation are the radiations most frequently used in the experimental production of mutations. These radiations also occur naturally are responsible for most of the spontaneous mutations. Ultraviolet radiations, with a wavelength of about 254 nm are strongly adsorbed by DNA and they exert their effect by the excitation of orbital electrons, raising them to their higher energy states. Sadava,H. and Berenbaum,H.C. state that the principle result of this exposure to UV light is the production of (usually thymine) dimers, two adjacent pyrimidine on the same DNA strand become cross linked together and so prevent normal replication.

Nutrient agar plates of
1. Staphylococcus aureus
2. Serratia marcescens
3. Escherichia coli (E. coli)
4. Pseudomonas aeruginosa
This experiment was done to acquire knowledge on the mutagenic effects of Ultra Violet (UV) light. The students worked in groups of four and to each group were given four agar plates with cell cultures which were after that exposed to UV radiation and its effects examined, so each group dealt with a specific species of bacteria/ organism. Four different kinds of bacteria were examined which are Staphylococcus aureus, Serratia marcescens, Escherichia coli and Pseudomonas aeruginosa.For each group four agar plates of the same organism were given so that each student in the group had one to examine. The first plate was used as a control and so was not exposed to UV light. The second plate was placed in the UV chamber with the cover lid taken off and the half of the exposed plate was covered with cardboard. The short wave of UV light was then turned on for exactly 30 seconds and then switched off before removing the cardboard and placing the cover lid over the plate again. The plate was then removed from the chamber. This procedure was repeated for the third plate and fourth plate but they were exposed to UV light for 90 seconds and 3 minutes respectively. The students made sure that their working areas were as sterile as possible by switch on their Bunsen burners for a safety flame. This action helps to sterilize the environment. The agar plates were then handed to the laboratory technicians for incubation. The plates were incubated for a week.

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