UV radiation Flashcards by Niamh Walsh

what is the measurement of UV, visable and IR radiation?

UV : 10 to 400 nm
* Visible : 380 to 780 nm
* Infrared : 700 to 1,000,000 nm (1 mm)

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how is UV light divided into ISO standard ranges?

– UV-A [400 –320 nm]
– UV-B [320 –280 nm]
– UV-C 280-100nm

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what does UV-C do?

it is completely blocked by the ozone layer

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what does UV-B cause?

sunburn and directly damages DNA

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what does UV-A do?

does not cause sunburn although still thought to contribute to skin cancer through free radical formation

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how is UV absorbed?

absorbed by nitrogen, oxygen, ozone and less than 5% of sunlight is in the UV
range at sea level

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what kind of vitamin is vitamin D?

fat-soluble secosteroids
essential for life
can be obtained from food and supplements

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what can happen if you are deficient in vitamin D?

deficiency can lead to bone-softening diseases
* rickets, osteomalacia, osteoporosis

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what does vitamin D increase absorption of?

Ca2+, Mg2+, PO43-

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what does vitamin D promote the biosynthesis of?

serotonin- increases mood

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what causes the body to produce vitamin D?

UV-B

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what is the most harmful type of radiation?

UV-C
completely absorbed in the ozone layer

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what damage does UV-B do?

eye damage, skin ageing/damage, sunburn, skin cancer (direct DNA damage)

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what does UV-A do?

– lowest energy
– not absorbed by the ozone layer
– does not cause sunburn
– does less biological damage, but not harmless
– eye damage, skin ageing/damage, skin cancer (indirect DNA damage)

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how does the different types of UV radiation penetrate the skin?

UV-A
– penetrates all the way through the skin to the dermis and subcutaneous layer
* UV-B
– penetrates through the Stratum Corneum to the Epidermis and dermis
* UV-C (if any were to reach the skin)
– would be entirely absorbed by the stratum corneum and epidermis

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how does UV-B cause DNA damage?

UV-B causes intramolecular reactions within DNA
– malignant melanoma (ca. 8% of cases)
– also possible with UV-A, but far less likely

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why are two adjacent thymine bases are specifically venerable?

– dimers are formed
– DNA strand is bent from normal shape, and cannot be read properly by

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UV-B causes the formation of cyclobutane pyrimidine dimers, what are these?

– strong covalent bonds link together two adjacent thymine bases (intrastrand)
– causes directDNA damage
– photochemical 2 + 2 cycloaddition
they disrupt DNA strand, so it cannot be accurately copied by DNA polymerase
and errors are introduced into the base sequence

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UV-B damage can also cause the formation of oxetan pyrimidiner dimers, what are these?

covalent bonds link together two adjacent thymine bases (intrastrand)
– the oxetane ring collapses to a pyrimidine-pyrimidonedimer
– causes directDNA damage
– initially, a photochemical 2 + 2 cycloadditio

what highly reactive substances can UV damage create?

highly reactive free radicals
- superoxide radical
hydorxyl radical

what are potential damaging reactions with cell constituents?

– Proteins, lipids in the cell membrane
– RNA and DNA in the cell nucleus

what UV light can produce free radicals?

both UV-A and UV-B can cause the production of free radicals

what do free radicals do to DNA?

free radicals cause indirect damage to DNA
they modify guanine base structure

what does a change in guanine structure cause?

causes mis-pairing
– normal : guanine pairs with cytosine (Watson-Crick pairing)
– mis-read : 8-oxoguanine pairs with adenine (Hoogsteenpairing)
– mis-pairing requires repair or can lead to mutations

what does DNA damage due to UV exposure under normal circumstances cause?

leads to the arrest of the cell cycle - DNA repair -apoptosis

what is an example for when apoptotic mechanisms decline with age?

if DNA repair or apoptosis does not occur then a genetic mutation will be carried through replication processes

what is the skin own sun protection granules? how are they made?

* The skin has its own sun protection granules -melanin – dark brown in appearance – made by melanocytes in the basellayer and are stimulated by direct UV radiation

what is the skin own sun protection granules? how are they made?

* The skin has its own sun protection granules -melanin – dark brown in appearance – made by melanocytes in the basellayer and are stimulated by direct UV radiation

after aprox 1 hour of exposure to sunlight, what appears on the skin?

melanin precursors appear in the skin – bleached melanin already in the skin darkens

how does delayed tanning work?

Delayed tanning occurs after ~2d exposure, peaking after 4-10d – UV radiation stimulates the production of melanocytes –this produces more melanin – increased cell division at the basal layer -> more keratinocytes which carry more melanin to the stratum corneum – stratum corneum becomes tanned and thicker offering more protection than untanned skin – full tan develops in about 14 days and lasts for the lifespan of the epidermis

how many different skin types are there?

6 type one fairest type 6- darkest

what mecanisms does direct damage caused by UV-B radiation trigger?

NA strands beyond repair trigger apoptosis * peeling to remove irreparable skin cells and inflammation responses – inflammation causes reddening through increased blood flow which makes the area warmer – release of prostanoidsand bradykinin lowers pain and heat receptor thresholds

how does skin damage affect aging?

constant DNA damage and repair causes natural errors in DNA replications causing signs of ageing * age spots –the constant triggering and suppression of melanocytes causes uneven pigmentation and spots

how does the skin elasticisty affect with aging?

elastosis -more noticeable in sun-exposed areas (solar elastosis) – leathery, rough, uneven skin textur

what is SPF?

Multiple by which a person can stay in the sun without burning/damage after applying the product compared to the time they could spend in the sun without burning/damage with no protection protect from UV-B for a certain amount of time

what does the star rating on sun cream measure?

measures UV-A protection scale of 5 starts

what are characteristics of a good suncream?

Bind well to the stratum corneum * Resist rub-off and wash-off by water and sweat * Are non-staining and non-toxic * Absorb light effectively over a broad spectrum at low concentrations to minimise risks of allergy and irritation.

how do chemical sunscreens work?

absorb UV radiation into their molecular structure without chemical change – high-energy (damaging) UV is absorbed by chromophores at specific wavelengths and then released at much lower energy that is not damaging blend of UV wavelengths

how do chemical sunscreens work?

what are physical UV- filters?

– have a high refractive index – reflect, scatter and may absorb UV radiation – titanium dioxide (UV-B) – zinc oxide0 and and b

how can you boost protection in UV filters?

auxiliary ingredients

what does effective UV protection require?

adherence to stratum corneum

what are film formers used for?

Film formers are used to create a hardy layer of UV filters on the skin – C20-40 alcohols, polyethylene, C30-38 olefin/isopropyl maleate/MA copolymer

what is the purpose of antioxidants?

free radicals are quenched by antioxidants

give example of antioxidants

– vitamin A, C, E – piperidine nitroxide (TEMPOL) – rutin(a flavonoid) – t-butylhydroxytoluene (BH