LAB WEEK 8 (Heat & UV light)

why is UV light so lethal?

because of its mutagenic properties

at what wavelength is UV light most germicidal?

260 nm

why is UV light most germicidal at 260 nm?

at this wavelength, DNA maximally absorbs UV light

pyrimidine dimers

when adjacent thymines or cytosines are covalently bonded together by UV light

what is the result of pyrimidine dimers?

DNA molecule becomes deformed, and DNA polymerase can no longer replicate strands past the site of dimer formation, nor can genes past this point be transcribed

Function of SOS system

enzymatic removal of dimer where new pyrimidine molecules are inserted in its place

what happens to the SOS system if there are a large number of pyrimidine dimers?

It cannot cope with this and begins making errors, which ultimately leads to cell death

T/F- Vegetative cells are more resistant to UV light than endospores

False

The killing properties of UV light depend on what factors?

1. Time of exposure

2. Presence of materials that block radiation from reaching cells

what surrounds the DNA of endospores?

small acid-soluble proteins that bind to DNA and alter its comfirmation, thus protecting endospores from photochemical damage

what does the spore photo product do?

performs enzymatic repair of damaged DNA in endospore formation

which B.megaterium culture, one in growth phase or stationary phase would survive better following UV light exposure?

Stationary phase- most bacteria would have formed endospores

thermal death point

lowest temperature at which a target population is killed in 10 minutes

thermal death time

shortest time required to kill a suspension of cells or spores under defined conditions at a given temperature

What factors can greatly influence results of TDT and TDP?

pH, moisture, medium composition, and age of cells

Which industry is TDT and TDP important?

food industry

Which two bacteria have endospores and are involved in food borne illness?

Clostridium botulinum and Clostridium perfringens

What do elevated temperatures do to proteins?

Cause them to denature and unfold

What makes endospores so heat resistant?

Calcium dipicolinate, low moisture content

T or F? Using new pipettes each time is not necessary.

False.

Why is UV light routinely used to sterilize surfaces?

It kills bacteria

Which organism had the highest temperature tolerance?

Bacillus subtilis

Can plastic and glass block UV radiation?

Yes

why does B. megaterium have a high thermal death point?

because it creates spores that are heat resistant

the shorter the wavelength, the more _______ it is to cells

damaging

T/F- B. megaterium is an endospore former

True

T/F- S. epidermidis is an endospore former

False

what are a few diseases caused by spore forming bacteria?

anthrax, gas gangrene, botulism, tetanus

UV light falls between ____ nm and ______ nm

4; 400

why is half of each plate covered with an index card?

to serve as a negative control