Wk 11: Causes of cancer - UV radiation (chemistry) Flashcards
What is vitamin D?
- Fat soluble secosteroids
- Inc intestinal abs of Ca, Mg + PO
- Promotes biosynthesis of serotonin
Deficiency of vitamin D can lead to what?
Bone softening disease:
- Rickets
- Osteomalacia
- Osteoporosis
What is serotonin?
- Monoamine NT
- Needed for: mood, cognition, reward, learning etc
- Production proportional to sunlight
What is UV-B needed for?
Produces vit D - 15 mins casual exposure
What is UV-C?
- Highest energy + most damaging
- Blocked by ozone
What is UV-B?
- Mostly abs by ozone
- Eye damage, skin ageing, skin cancer
What is UV-A?
- Lowest energy
- Not abs by ozone
- Doesn’t cause sun burn
How much does UV-A penetrate?
Through skin to dermis + SC layer
How much does UV-B penentrate?
Through stratum corneum to epidermis + dermis
How does UV-B cause DNA damage?
Causes reactions w/in DNA - forms dimers
What are dimers?
DNA strand bent from normal shape + cannot be copied by DNA polymerase
What are the 2 dimers UV-B can form?
- Cyclobutane pyrimidine dimers (80%)
- Oxetane pyrimidine dimers (20%)
How does UV-B form cyclobutane pyrimidine dimers?
- Strong covalent bonds link 2 adjacent thymine bases
- Cause direct DNA damage
- Photochemical 2 + 2 cycloaddition
How does UV-B form oxetane pyrimidine dimers?
- Covalent bonds link 2 adjacent thymine bases
- Oxetane ring collapse to pyrimidine-pyrimidone dimer
- Causes direct DNA damage
How else can UV light cause DNA damage?
Creates highly reactive free radicals:
- Superoxide radical
- Hydroxyl radical
Modifies guanine bases - causing indirect DNA damage
What do free radicals damage within cells?
- Proteins + lipids in membrane
- RNA + DNA in nucleus
What is watson crick pairing?
Normal: guanine w/ cytosine
What is hoogsteen pairing?
8-oxoguanine pairs w/ adenine
What happens to apoptotic mechanism as you age?
Declines: more likely for mutations to be carried (cutaneous tumorigenesis)
What is melanin made from?
Melanocytes in basal layer + stimulated by direct UV radiation
What occurs in delayed tanning (2 days exposure)?
- Peak 4-10 days
- UV radiation stims prod of melanocytes = more melanin
- Inc cell division at basal layer = more keratinocytes = more melanin to stratum corneum
- Stratum = tanned + thicker for more protection
What is type 1 skin?
- Pale
- Light eyes
- Blond/red hair
- Always burns, no tan
What is type 2 skin?
- Fair
- Light eyes
- Burns easily, may tan
What is type 3 skin?
- Medium
- Initially burns then tans
What is type 4 skin?
- Light brown
- Tans w/ minimal burns
What is type 4 skin?
- Medium brown
- Rarely tans
What is type 6 skin?
- Dark
- Easily tans + never burns
What are the defence mechanisms of the skin after direct damage to DNA by UV-B radiation?
- Apoptosis: peeling + inflammation
- Inflammation: red through inc blood flow
- Release of prostanoids + bradykinin: lowers pain + heat receptor threshold
What happens to the skin after frequent exposure to the sun?
- Age spots: constant trigger + suppression of melanocytes = uneven pigmentation
- Elastosis: constant change in connective tissue reduce skin strength
What is sun protection factor?
Multiple by which person can stay in sun w/o burning w/ product compared to time spent in sum w/o burning w/ no product
How doe sunscreens minimise the risk of allergy + irritation?
Absorb light over broad spectrum at low conc
What are chemical sunscreens?
- High energy UV abs by chromophores at specific wavelength + released at lower energy - no chemical change
- Aromatics conjugated w/ carbonyls
What are physical UV filters?
- High refractive index
- Reflect UV
Give examples of physical UV filters
- Titanium dioxide (UV-B)
- Zinc oxide (UV-A/B)
What are film formers?
Used to create hardy layer of UV filter on skin:
- C20-40 alcohols
- Polyethylene
- C30-38 olefin
What is used to prevent cellular damage by free radicals?
Antioxidants:
- Vit A, C + E
- Piperidine nitroxide
- Rutin
- BHT
How do anti-inflammatories help slow the progression of skin damage by UV radiation?
Stop biological cascade reaction:
- Red reddening, pain, blister + peeling
- However doesn’t stop DNA damage
