4Thurs_Lethal effects of UV

4Thurs_Lethal effects of UV - Lab Exercise: Lethal effects...

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Lab Exercise: Lethal effects of ultraviolet light OBJECTIVES 1. To understand the mechanism by which UV light causes damage and how this can lead to cell death. 2. To perform experiments to test the varying resistance to UV light of different microbes INTRODUCTION UV light is nonionizing short wave-length radiation that falls between 4 nm and 400 nm in the visible spectrum. Most bacteria are killed by the effects of UV light and it is routinely used to sterilize surfaces, such as work areas of transfer hoods used for the inoculation of cultures. The primary lethal effects of UV are due to its mutagenic properties . When DNA absorbs UV light, it causes the formation of pyrimidine dimers . These form when a covalent bond forms between two adjacent thymine or cytosine molecules in a strand of DNA. These dimers deform the DNA molecule, so that DNA polymerase is unable to replicate the strand of DNA past the site of dimer formation and genes can no longer be transcribed. Cells have evolved various repair mechanisms to deal with the damage (including
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4Thurs_Lethal effects of UV - Lab Exercise: Lethal effects...

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