ultraviolet light

frequency

number of crests that pass a given point within 1 sec

once wave

1 Hertz

long wavelength

low frequency, low energy

short wavelength

high frequency, high energy

Characteristic of ultraviolet light

• non-ionizing

• lower energy than gramma and x-ray

how many nm is ultraviolet light

4-400 nm

gamma and x-ray is effective for sterilizing

heat sensitive objects

what is the maximum killing wavelength of bacteria

260nm

what are the lethal effects of UV on bacteria

destruction of the DNA

Why is UV light most effective at 260nm?

DNA absorbs maximum light at UV 260nm and formation of pyrimidine dimers

killing properties of UV light depend upon

time of exposure and blocking materials

results of UV

plastic and spores protect the organism from the lethal effects of UV light

B. Subtilis effects after 10 sec of UV exposure

abundant growth

B. subtilis when exposed to 30 sec of uv

moderate growth

S. marcescens after being exposed to UV for 10 sec

moderate growth

S. Marcescens after exposed to uv for 30 sec

slight growth

B. subtilis and S. marcescens after exposure to UV for 30 sec with lid on

growth the same as the control group

pyrimidine Dimers

DNA polymerase

thymine dimer

two t have formed double bond with each other

Aerobic respiration recall

oxygen is used as a terminal acceptor of electrons to make H20

if bacteria produces the enzyme catalase

convert H2O2 to water and oxygen