Uskrsnuće po Radmanu
#1
Posted 29 September 2006 - 13:56
Both desiccation and radiation break D. radiodurans's chromosomes into short DNA fragments. Radman and his colleagues blasted the microbe with one megarad of gamma radiation, enough to sterilize food but well below D. radiodurans's resistance threshold. Nevertheless, its chromosomes broke down into short strands of DNA. For the next hour and a half, the cells appeared dead, but by the end of three hours the chromosomes of D. radiodurans were reassembled and fully functioning.
Close observation of this miracle revealed that DNA synthesis was at work, in which each fragment serves as a template and extends itself by removing damaged ends and overlapping with a fragment that matches part of its sequence of nucleotides--all with the help of an enzyme known as PolA. Ultimately this results in single long strands of repaired DNA, as much as 30 times longer than the longest repetitive sequences of D. radiodurans's DNA.
But such single long strands of DNA do little to resurrect the microorganism until the second stage of the newly discovered process kicks in: the simple pairing discovered by Watson and Crick decades ago--adenine (A) bonds with thymine (T), and cytosine © bonds with guanine (G). By inserting a special version of the nucleotide thymine that only binds to single strands of DNA--known as 5-bromodeoxyuridine--the researchers could observe as the single strands bonded with complementary strands to form complete chromosomes. "Once the chromosome is functional, the synthesis of all cellular components starts, and the cellular life is back," Radman says.
The process--dubbed extended synthesis-dependent strand annealing--solves the mystery of how D. radiodurans survives radiation and repairs the damage it causes, according to the paper presenting the result published online in Nature on September 28. It also shows that the plucky microbug actually synthesizes DNA faster during such recovery than during its own normal replication. But it does not solve the mystery of how common enzymes, such as PolA, work so much better in D. radiodurans than in other microorganisms that radiation kills for good, notes Michael Daly of the Uniformed Services University of the Health Sciences.
Regardless, scientists are now closer to understanding the remarkable strength of this "strange berry" and perhaps putting it to work. "Because Deinococcus can survive death, I like to dream that it can teach us how to resurrect dead neurons," Radman says. "Plus, I would send [it] to seed life on sterile planets--directed panspermia." A big role may await this tiny extremophile.
link
#2
Posted 30 September 2006 - 03:08
Sjajno!
#3
Posted 30 September 2006 - 19:16
#4
Posted 30 September 2006 - 19:24
Super za jednocelijske organizme ali mislim da je totalno neprimenjivo za nesto vise od toga.
Edited by Jr, 30 September 2006 - 19:43.
#5
Posted 01 October 2006 - 02:53
#6
Posted 01 October 2006 - 04:40
Sjajno!
Sir Indi, si ti bas siguran da nam je ovaj Miroslav Radman(ovic) zet.
Nesto se ovi nasi sve vise muvaju po genetici i genetskom inzenjerstvu. Da ne naprave neko sranje!?!
Lep pozdraU.
#7
Posted 01 October 2006 - 13:45
?
Radman je hrvat, inace radi i u Zg, gledao sam pre neki dan intervju na hrt.
#8
Posted 01 October 2006 - 14:01
pa to ga ne sprecava da bude forumski zet, kao u asteriksu (epizoda razdvojeno selo).
#9
Posted 01 October 2006 - 18:15
ma nma vz, pogresno skontah Svaka cast coveku sto je otkrio.
#11
Posted 04 October 2006 - 12:10
Nesto sam citao o njegovim otkricima tako da mogu da dam neko svoje misljenje o Radmanu. Njegov najbolji rad (koautor) je citiran otprilike 250 puta sto govori da je kao naucnik nesto bolji od proseka. Njegove hipoteze o selekciji vrsta koje izvodi na osnovu enzima koji ucestvuju u ispravljaju gresaka pri replikaciji su malo pretenciozne. To sto neki enzimi nemaju veliku selektivnost i kataliticku efikasnost ne znaci da ti enzimi uslovljava nekakve "dirigovane" mutacije. Pod uslovom ako je procitao baj jednu knjigu iz enzimologije video bi da transformacija substrata zavisi od parametara kao sto je temperatura, koncetracija substrata, kataliticke efikasnosti enzima itd. Na kraju, na osnovu onoga sta prica mogu zakljuciti da je dobar za marketing...
#12
Posted 04 October 2006 - 12:42
strahotno...
Edited by Indy, 04 October 2006 - 13:52.
#13
Posted 04 October 2006 - 15:05
Svrha nekog naucnog rada nije da pokaze kako je autor bio pametniji od drugih, nego da pokaze da li neka hipoteza vazi i u praksi. Jedino sto je tu pretenciozno je sto ta istrazivanja zahtevaju puno finansijske potpore.
On pokusava da objasni mehanizam necega sto postoji kao hipoteza vec duzi niz godina i odnosi se na slobodne mutacije koje nisu uslovljene dejstvom agensa iz spoljasnje sredine.
#14
Posted 04 October 2006 - 15:07
A zasto je to "pretenciozno"?
#15
Posted 04 October 2006 - 15:34
Njegove hipoteze o selekciji vrsta koje izvodi na osnovu enzima koji ucestvuju u ispravljaju gresaka pri replikaciji su malo pretenciozne. To sto neki enzimi nemaju veliku selektivnost i kataliticku efikasnost ne znaci da ti enzimi uslovljava nekakve "dirigovane" mutacije. Pod uslovom ako je procitao baj jednu knjigu iz enzimologije video bi da transformacija substrata zavisi od parametara kao sto je temperatura, koncetracija substrata, kataliticke efikasnosti enzima itd. Na kraju, na osnovu onoga sta prica mogu zakljuciti da je dobar za marketing...
zapravo 479 (ISI na danasnji dan).
sto isto nije nesto neuobicajeno za najcitiraniji rad (mada ne verujem ni da je 250 malo iznad proseka, ne znam na kojoj si populaciji usrednjavao), ali ta jedna cifra generalno jako malo govori.
recimo bill phillips jos uvek nema nista preko 325, a u trenutku kada je dobio nobela kljucni rad nije imao ni 200.
statisticka analiza kumulativnog impacta je generalno komplikovana stvar i podlozna raznim kontraverzama. jorge hirsch je nedavno formulizovao prilicno elegantan i inteligentan pristup quick assesmentu, koji naravno opet ima mana i (skoro) nista ne znaci medju insiderima, ali je makar superioran citiranosti najcitiranijeg rada, da ne govorimo o (tradicionalno pogubnom) brojanju radova. (radmanov h-index je na danasnji dan 49)
ova druga tema je jos mnogo komplikovanija, nemam sad vremena.