Radiation Effects 💫 Flashcards
Describe the effects of low energy (non-ionising) radiation on the human body?
-Thickening of epidermis
- darkening of existing pigmentation
- new pigment formation = melanin
- increased reactive oxygen species in skin
- increased TNFa
- proliferation changes in epidermis
- suppression of T lymphocytes
Which rate- limiting enzyme do sunscreens increase?
Sunscreens increase
Ornithine decarboxylase activity
What affects does UVA radiation have:
Contributes to:
Immune suppression
Pigmentation
Signs of ageing
What are the common structural features of photosensitisers?
- low molecular Weight (200-500)
- planar, tricyclic or polycyclic
- often contains heterostoms: stable resonance structures
- all absorb UV/ visible radiation
What do Photodynamic Action include?
3
- Internal conversion
= interaction between energy levels
= molecules can dissipate energy cua vibration relaxation and returns to original state.
No chemical change to molecule - Fluorescene
- Phosphorescence
What is Fluroescence?
Molecule gives up photon of light as it returns to ground state
What is Phosphorescence
Molecule gives up photon of light as it returns to ground state from triplet excited state
What are the acceptors of photodynamic action?
Proteins
Lipids
carbohydrates
Nucleic acids
Acceptors of Photodynamic action
Explain the action of
PROTEINS
Amino acids eg. HISTIDINE:
TYPE 2 REACTION
Imidazole ring reacts with O2 adding O2 across across double bond, forming an unstae cyclic intermediate which subsequently breaks down = histamine gets damaged
Acceptors of Photodynamic action
Explain the action of
LIPIDS
Type 2 reaction:
O2 adds across double bond of lipid molecule
Lipids are found in cell membrane, reaction leads to disruption of cell membrane and cell death
Acceptors of Photodynamic action
Explain the action of
CARBOHYDRATES
Type 1 reaction
Eg. Sugars, alcohol, vitamins
Contain many hydroxyl (OH)s which interact with the triplet excitesstate giving a free radical reaction!!
Acceptors of Photodynamic action
Explain the action of
NUCLEIC ACID
Type 2 damage
Eg. Purines
Purines can be oxidised and therefore are susceptible to attack by singlet oxygen.
Photosensitisation reaction
Diagram
Photochemical reactions
5
Diagram
Cellular defence mechanisms
Name chemical and enzymatic defences=
Chemical=
- vitamin C and E: natural antioxidants
- uric acid: scavenger of singlet oxygen and radicals
- glutathione: protects mitrochondria from free radicals
Enzymatic=
- superoxide dismutase:
Catalyses reaction of toxic superoxide radical
- catalase:
- reduces hydrogen peroxide (HOOH)
- glutathione peroxidase (GPx) which reduces lipid peroxides and hydrogen peroxides
