Ex. 17 Ultraviolet Radiation and Photoreactivity
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electromagnetic spectrum
all forms of radiation categorized upon nrg and wavelength
UV (non ionizing radiation) wavelength is
15-390 nm
DNA mutations
can be caused by UV radiation. sudden inheritable or lethal changes in genetic material
are wavlengths below 200nm dangerous
no because they are absorbed by air. therefore do not reach organisms
germicidal
lethal wavelength UVC 200-290 nm.
why is germicidal lethal
correpsonds to optimal absorption wavlengths of DNA. 260 nm peak of germicidal actvitiy
UVB wavelengths
290-320 cuase damage to DNA as well
UVA wavelengthhs
320-400 nm. not as readily absorbed, less active on living organisms
pyrimidine dimers
extra bonds between adjacent thymine or cytosine bases. formed when DNA absorbs UV radiation, nrg forms the dimers
what is the fn of pyrimidine dimes
distort DNA structure preventing base pairing during DNA replication and transcription. DNA not copied properly, faulty gene product. cell can die
are pigmented and endospore forming bacteria resistant to UV
yes they are more resistant to the effects of UV radiation than other species
dark reactivation
enzymes acting in dark, repairs damage caused by UV
photoreactivation (light repair)
enzymes repair damage caused by UV by immediate exposure to bright light.
can reactivation enzymes repair DNA if does of UV is too high
no. cells are unable to divide, there is more damage to DNA than enzyme can repair
can UV be used as a sterilizing agent? why or why not
no unable to penetrate glass, plastic, water, blood etc. poor penetrating ability
UV can decontmainate
air and surfaces only
another disadvantage of UV sterilization
damages human eyes and skin. but lamps used in labs, hospital rooms where humans are shielded