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<br /> <:a~'~'~~ Part 2. * Boma Intt-od,actary Information
<br /> .i ,~,Ys•',,.
<br /> * Assertians in this communication era supported in
<br /> detail, and with very epacifio sa,arcing, in C~cfman 1990 (~haptars
<br /> 1u", 19, 20, 21, 32, 33'.
<br /> T}1.=r? Is `wo Saf? Threshold For E::t%c•s,ar? To Lcw-Doses Radiation (p7 ct" 34'
<br /> a. * Cancers require the presence of damaged genetic
<br /> malecules .r. the _tnc,la ,_e:is which :urn malignant. Likawls-=,
<br /> inhal'it?~_; aff 1 is=.ions r?quir? the pr?serge of c]ama<;?d .gene` _c
<br /> Cm_,1P U.,=_. *t~a =.in,~~l? ;=iii ir,-.m a], i,Lal a 1?`~y ;j a, .7•P72. qen:-ti,_
<br /> mcleculas a human, _~L-nue leu_: ate rh? !~6 human chrom~sc~.e<-,, aac't;
<br /> c,r~- -•ubl--=_I':anci uNA he1i:• pJlus as=_ciat?rl Mains.
<br /> r. * After damage occurs to a genetic molecule, the cell
<br /> attampr.,s to repair it. If r.};a ,?il ~achi,=ve: perfart• repair, the
<br /> ganeL iC mG i2C,],la I'PC;a Ir,_: 1'° ':'fi3r, dual it j~~~ a_; ;~O ~7=_e ye 17ad
<br /> + The menace t~•}~~alth invalves the genr-.tic -Damage
<br /> which is unrepaired, unrepairable, ar misrepaired. Tile °~.~:blesome
<br /> tri=.
<br /> * Whan the damage is c,~mplex for example, when
<br /> the opp~sit? strands of the double he_li:c have been broken pieces
<br /> of the DNA do,~ble-helix sometimes and up in the wrong place, or
<br /> become permanently lost. These i~aiiuras cf~ repair are not
<br /> ih?ra Is i1o Safe Threshold For ;=.!pos,.~re T•-~ Low-Dose Radiation (p3 of '_,4~
<br /> disput?.
<br /> * By contrast, the cell is exquisitely efficient at
<br /> repairing injury to single strands of the double helix. It bees beer,
<br /> =st•im•ate<1 that., every day, each ,~e11 cepas wir.h at• least _ . , i00 DNA
<br /> injuries in ]u ed by routine rhPmicai aounces (including fry
<br /> radials 9r b _ed by '-h? •_eli ,sel: Such standard repairs mrg}it.
<br /> ba compared to raplar:ing a lamp':; hrol~en Iight bulb with a r,aw bulb.
<br /> Af~tar "rapai°. the lamp wor~}.;~ par-feor_.ly again.
<br /> y . ~;-,:......ad;at+on has' demonstrated bevand any
<br /> .5~y,ubt i~•~ abilit•v tc break both strands of the DNA_dauble :Ielrx at
<br /> t}'te same time. •I'his ability has made it "famous" among tux:- agents
<br /> as a chromosamo-breaker: (If anly one DNA's*,rand breaks,,the other
<br /> strand holds the chromosome together t)
<br /> ,a, * i;ount•1?ss axpertm?n*..s have been done on cail.=_. to
<br /> measure the spaced with which they repair radiation-induces DNA
<br /> c]amaga, br:t.h single-st•rand and double-strand injuries, Even after
<br /> extremely high radiation doses, that repair which does occ-.r is
<br /> complete within. about & hours, and most of it is aamplere within
<br /> about. ~ hours.
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