solar uv radiation
DESCRIPTION
Solar UV Radiation. UVCTRANSCRIPT
Solar UV Radiation
• UVC <290 nm Absorbed by ozone
• UVB 290 – 320 nm ~0.5 % total energy
• UVA 320 – 400 nm 6% total energy
UV Spectrum of DNA
250 300Wavelength (nm)
Absorbance
Pyrimidine Photodimers
NH
NH
NH
NH
CH3CH3
H H
O
O
O
O
NH
NH
NH
N
CH3H
H H
O
O
NH2
O
N
NH
NH
N
H H
H H
NH2
O
NH2
O
T<>T T<>C C<>C
N
NH
NH
NH
O
O
CH3
O
H
NH2
N
NH
NH
NH
O
O
CH3
O
H
OH
CH3
T(6-4)C T(6-4)T
Bipyrimidine (6-4) Photoadducts
DNA Photooxidation Mechanisms
P
P*Type II
O2
1O2 singlet oxygen
DNA
G Oxidation
hν
Type I
DNA P-. + DNA+.
Hole Transfer
Oxidation atGG(A) doublet
N
N
H2NN
N
NN
N
HN
HHO
N
dR
N
dR
O OH2N
H2N
H
dR
O
O O
Imidazolone Oxazolone Spiroiminodihydantoin
N
N
S
HO3S
H
HOOC
SUPROFEN
PBSA
O
32P-DNA + PSUV irradiation
EtOH precipitation
Piperidine
Electrophoresis
Autoradiography
Upturned Eppendorf lid
Method of irradiation and visualization of DNA damage
Single-stranded DNA
• Singlet oxygen
• UV dose & [SP] dependent
Uniform G-specific attack
Quenching in ss DNA
1 SP + UVB
2 & 3 Quenched by sodium azide & DABCO
4 & 5 Mannitol & SOD have no effect
Singlet oxygen damage in ss DNA increases in D2O
H2O
D2O
Duplex DNA
Specificity for 5’-G of 5’-GG-3’ doublets
5’-G of 5’-GA-3’ doublets
Conclusions
• Single-stranded DNA - Type II mechanism– singlet oxygen
• Duplex DNA - Type I mechanism– electron transfer - DNA to excited sensitizer– hole migration
MALDI-TOF Analysis of DNA
• Requires picomole amounts of sample
• Mass accuracy to ~0.1%
• Generate +ve and –ve ion spectra
• UV-absorbing matrix for <100 base pairs
• Applications in DNA sequencing