UV radiation Flashcards
3 types of UV light and what they do
UV-A: doesn’t cause sunburn but can still cause skin cancer through free radical formation, lowest energy, not absorbed by ozone layer, less biological damage, indirect DNA damage
UV-B: causes sunburn and directly damages DNA, mostly absorbed by ozone layer, eye damage, skin/ageing, sunburn/cancer, direct DNA damage
UV-C: completely blocked by the ozone layer, highest energy and most damaging
benefits of UV-B
causes body to produce vitamin D
need some UV-B radiation to maintain adequate vitamin D levels
15mins sun exposure a few times a week
How the UV lights are abrorbed by the skin?
-> WAVELENGTHS
UV-A: penetrates all the way through skin to dermis and SC layer
UV-B: penetrates to epidermis and dermis
UV-C: doesn’t reach skin, but would be absorbed by stratum corneum and epidermis
What type of damage does UV-B cause?
intramolecular reactions with DNA
2 types of dimers that UV-B can cause?
- cyclobutane pyrimidine dimers 80%
- oxetane pyrimidine dimers 20%
How do cyclobutane pyrimidine dimers occur from UV-B?
strong covalent bonds link together 2 adjacent (on same strand) thymine bases - intrastrand
causes direct DNA damage
disrupts the DNA strand so it can’t be copied by DNA polymerase
- errors introduced into the base sequence
oxetane pyrimidine dimer formed from UV-B
covalent link together 2 adjacent thymine bases (intrastrand)
the oxetane ring collapses to a pyrimidine-pyrimidone dimer
causes direct DNA damage
indirect damage, especially by UV-A
formation of free radicals
2 types of free radicals that can be formed that damage DNA
superoxide radical
hydroxyl radical
What can free radicals interact with and damage?
proteins, lipids in cell membrane
RNA, DNA in nucleus
What type of damage do free radicals cause DNA?
indirect damage
What type of UV light can cause formation of free radicals?
UV-A and UV-B
What do free radicals interact with in body?
guanine
What is formed from interaction between free radicals and guanine?
8-oxoguanine
-> occurs indirectly
What can happen with 8-oxoguanine?
8-oxoguanine pairs with adenine - Hoogsteen pairing
this mis-pairing requires repair ir can lead to mutations
What is the Hoogsteen pairing?
pairing of 8-oxoguanine to adenine
apoptotic mechanisms and age
apoptotic mechanisms decline with age
sun protection granules in the skin
melanin
made by melanocytes in basal layer and stimulated by direct UV radiation
What UV radiation causes sun burn from direct damage to DNA?
UV-B
What is the constant triggering and suppression of melanocytes that causes uneven pigmentation and spots called?
age apots
What is leathery/rough/uneven skin texture called?
elastosis
SPF
sun protection factor
2 factors in sun cream
SPF
star rating
What is SPF and what does it do?
multiple by which person can stay in the sun without burning/damage after applying the porduct compared to the time they could spend in the sun withoug burning/damage with no protection
protects skin from harmful effects of UV-B radiation for a specific amount of time
What does SPF protect from?
UV-B
What does star rating protect from?
UV-A
How do the organic UV filters in sun creams work?
absorb UV radiation by chromophores at specific wavelengths and release it at a much lower energy that is not damaging
What types of organic UV filters are used in sun creams?
aromatics conjugated with carbonyls
How do inorganic UV filters in sun cream work?
physical UVfilters
have high refractive index
reflect, scatter and may absorb UV radiation
examples of UV inorganic filters used for UV-A and UV-B
UV-A: zinc oxide
UV-B: zinc oxide, titanium dioxide
What should good sun cream contain?
combination of inorganic and organic UV filters
What do film formers do in sun cream?
used to create a layer of UV filters on the skin
adherance to straum corneum
resistance to water/sweat/rub off
What do antioxidants do in sun cream?
absorb free radicals on the skin surface
free radicals formed by UV radiaiton
examples of antioxidants
Vit A, C, E
piperidine nitroxide
rutin (a flavonoid)
BHT - t-butylhydroxytoluene
What do anti-inflammatories to in sun cream?
slow progression of UV damage leading to skin damage
interfere with skin response to damage by stopping the biological cascade reaction
reduce reddening, pain, blistering, peeling effect of sunburn
doesn’t stop DNA damage so ageing/cancer can still progress
