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F. Scappini (2), M. Franchi (3), E. Gallori (3), C. Cecchi-Pestellini (4), M. Barbera (1),

The Role of Clays in Shielding DNA against X-Ray Radiation: Possible Implications on the origin of life Angela Ciaravella. F. Scappini (2), M. Franchi (3), E. Gallori (3), C. Cecchi-Pestellini (4), M. Barbera (1),

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F. Scappini (2), M. Franchi (3), E. Gallori (3), C. Cecchi-Pestellini (4), M. Barbera (1),

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  1. The Role of Clays in Shielding DNA against X-Ray Radiation: Possible Implications on the origin of life AngelaCiaravella • F. Scappini (2), M. Franchi (3), E. Gallori (3), C. Cecchi-Pestellini (4), M. Barbera (1), • R. Candia (1), G. Micela (1) • INAF – Osservatorio Astronomico di Palermo , Italy • ISMN –CNR , Bologna, Italy • Dipartimento di Biologia Animale e Genetica, Univ. di Firenze, Italy • Dipartimento di Fisica, Univ di Lecce, Italy Firenze 28/02 – 1/03/05

  2. Conditions on the Early Earth How and under which conditions life was created? First evidence of life on the Earth 3.8 × 109 yr Earth Atmosphere : a big unknow, very little screening from Sun radiation Early X-ray Sun: more active, hard and bright 3 × 1026 (0.1 keV) < Lx >= 1027 erg/sec 5 × 1027 (0.2 keV) Yohkoh-SXT 3-40 Å band 1-10 keV band: the photon flux today is ~10-3 the flux at the age of Pleiades Sun @ max Sun @ min

  3. B A 34 Å per turn 27-28 Å per turn DNA Irradiation Why DNA? DNA is already life  An easy and well tested method to estimate damage We irradiate free and clay absorbed DNA from Bacillus Subtilis CLAYS: Montmorillonite Na0.2Ca0.1Al2Si4O10(OH)2(H2O)10 Kaolinite Al2Si2O5(OH)4 Free DNA type B Clay Adsorbed DNA type A

  4. DNA X-Ray Irradiation Line (keV) Flux (erg sec-1 cm -2 ) Al 1.49 0.15 Ti 4.51 0.17 Cu 8.04 0.20 10-5 minimum 3 × 10-3 maximum 10-1 large flares The Sun today (1.5 –12.4 keV): DNA Samples: Free 10μg DNA + 1400l of H2O Clay Adsorbed 10μg DNA + 2mg Clay + 1400l of H2O The XACT Facility: X-ray, UV, Vis 2 -104 eV (1- 7000 A). 17 m stainless-steel vacum beam line class 1000 clean_room (Barbera et al 1999). Vacuum tight container Irradiation Dose : 102-5.8 × 104 erg Exposure Time : 2m - 16h

  5. DNA Damage Evaluation Transformation frequence for non irradiated DNA The integrity of DNA molecules is estimated by transformation experiments : efficiency of irradiated DNA to transform competent cell in a bacterial culture The transformation frequence is: Typical errors onFtf are 20 % Comparing Ftf with Ftf0 the damage is evaluated

  6. Results and Conclusions I ⃟ ⃟ ⃟ ⅏ ⅏⅏ Clay Adsorbed DNA is resistent to the X-ray irradiation The more compact configuration (A) of clay adsorbed DNA binding to the substrate by electrostatic and/or hydrogen bonds can play protective role *** Free DNA is severely damaged by X-rays and the damage depends on the energy dose rather than the hardness of radiation Can clays shield DNA against X-rays? Diluted clay is much more transparent than H2O to X-rays

  7. Results and Conclusions II 2.5 mm Num X photons (Cu 5 × 104 erg) 4 × 1012 Num H2O molecules 5 × 1022 Num DNA molecules 4 × 1011 1 mm 0.2 mm 0.01 mm Are X-rays directly responsible for DNA damage? Secondary UV UV irradiation of free and clay adsorbed DNA give similar results(Scappini et al 2004) DNA adsorbed on clays do survive X-rays and UV photodegradation Are clays essential in protecting the basic building blocks of life as well ?

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