effect of ultraviolet on bacterial cells Biology and Biotechnology department

purpose this lab demonstration to: illustrate the effect of ultraviolet on bacterial cells. 2. Observation the ability of ultraviolet radiation to penetrate cells and other matter. 3. The ability of bacteria cells to repair UV damage.

principle Ultraviolet radiation is part of the electromagnetic spectrum , but with shorter , higher energy wave length than visible light . Because the DNA absorb UV radiation , prolonged exposure can be lethal to cells.

Studies have shown that when DNA absorbs UV radiation , the energy is used to break the bonds between the strand and form the new covalent bonds between adjacent pyrimidine's EX: Ether cytosine _ cytosine , cytosine –thymine , or more typically thymine_ thymine (thymine dimers). thymine dimers :- Distort the DNA molecule and are incapable of base-pairing DNA replesment .

If enough genes possess thymine dimers and the subsequent mistakes, faulty gene products will be mad and the result can be death for the cell. Many bacteria have mechanisms of repair such DNA damage . Light repair Dark repair Repair the thymine dimers and replacing with two other thymine.