Lab 12 - Effect of UV Radiation on Bacterial Growth

What is the spectrum of UV light?

10 nm to 400 nm

Why was there still E. Coli after UV exposure? How can we explain this result?

Did see growth. But with increased exposure, less growth. At 80s, no growth. E. Coli still has repair mechanisms for UV radiation, which is why we saw it have growth will shorter exposure.

Why was it important to remove lid on plate?

For direct exposure

Was there a difference in the amount of growth of D. radiodurans after 10s, 20s, 40s, and 80s of UV exposure?

No. There was the same amount of growth on the control side as was on the exposed side. To see a reduction of D. Radidurans growth we need longer exposure. Thyamine Dimer formation mechanisms.

What was the control in this experiment?

The control was the side of plate that was NOT exposed to UV light.

What happens if organism is unable to repair thymidine dimer?

They can kill that cell or disable it to prevent it from replicating.

What forms in the DNA from radiation?

Thymine Dimers - bonding between adjacent thymine bases in the DNA.

What is the purpose of this lab?

To examine the killing effect of ultra violet (UV) radiation.

What were results?

With increased time exposure to UV light, E. Coli formed less colonies. There was no change in growth with time of exposure for D. radiodurans. Same amount of growth as the control side.

What is ultraviolet germicidal irradiation (UVGI)? -where is it used?

a disinfectant method that uses UV radiation to kill or disable microorganisms. -food and beverage production, wastewater treatment, air purification

What is photoreactivation?

enzymes break the covalent bonds in the dimer, restoring the DNA to its original confirmation.

What is excision repair?

enzymes exise the thymine dimer and the gap left by the excised DNA is then filled in and seales by DNA polymerase and DNA ligase, respectively.

What two organisms did we study? -how do we test them?

(1) E. Coli (2) Deinococcus radiodurens (highly resistent to radiation) means radio activity. Why? Because it has more forms of DNA repair. Therefore less sensitive to UV radiation. -created lawns of bacteria on plate.

How is something resistant to radiation?

-any form of repair (that we discussed in lecture) -expression of these genes are increased in these bacteria