On 22 Maj, 11:02, p...@RQNNE.invalid (Per Rønne) wrote:
> Poul E Hansen <o...@ofir.dk> wrote:
>
> > On 21 Maj, 14:46, Dybbøl <dybb...@hotmail.com> wrote:
>
> > > I dagens radioavis kl 12.00 talte man med en forsker fra DTU om det. Han
> > > mente at når man kalder det at "skabe liv" kan det sammenlignes med at
> > > kalde et gebis for tænder! Ha ha - forlorne tænder, forloren intelligens
> > > og forloren skabelse!
>
> > Han sammenlignede 'kunstigt liv' med kunstige tænder. Hans forklaring
> > var vist, at de gener / gen-grupper man kunne finde på at sætte ind,
> > er nogle der allerede er kendt fra eksisterende organismer, d.v.s. der
> > er tildels tale om efterligninger af noget der findes i forvejen.
>
> > Hvis kunstigt liv skal betyde, at mennesker skaber liv ud noget dødt,
> > falder den kunstige celle uden for kategorien, da den var levende i
> > forvejen.
>
> Cellen »døde« da man fjernede kromosomerne fra den; den blev igen
> levende, som en anden celle, da man satte nye, kunstigt frembragte
> kromosomer ind i den.
Ja - cellen døde, ingen tvivl om den ting. Man kan indvende, at man
havde brug for en levende celle for at udføre eksperimentet. Og på den
måde, har man da ret - det er endnu blot delprocesser. Men alt
understøtter og arbejder indenfor den tese, der er formuleret omkring;
Biogenesen.
Dr findes så andre - delprocesser, hvor der arbejdes netop med
konstruktionen af cellemembranen - RNA etc. Jeg har linket til et par
eksempler tidligere, hvor indvendingerne netop har lydt sådan. På et
tidspunkt samles trådene fra de forskellige laboratorier utvivlsomt -
Evolution in an RNA World
G.F. Joyce
+ Author Affiliations
Departments of Chemistry and Molecular Biology and the Skaggs
Institute for Chemical Biology, The Scripps Research Institute, La
Jolla, California 92037
Correspondence: gjo...@scripps.edu
A long-standing research goal has been to develop a self-sustained
chemical system that is capable of undergoing Darwinian evolution. The
notion of primitive RNA-based life suggests that this goal might be
achieved by constructing an RNA enzyme that catalyzes the replication
of RNA molecules, including the RNA enzyme itself. This reaction was
demonstrated recently in a cross-catalytic system involving two RNA
enzymes that catalyze each other’s synthesis from a total of four
component substrates. The cross-replicating RNA enzymes undergo self-
sustained exponential amplification at a constant temperature in the
absence of proteins or other biological materials. Amplification
occurs with a doubling time of ~1 hour and can be continued
indefinitely. Small populations of cross-replicating RNA enzymes can
be made to compete for limited resources within a common environment.
The molecules reproduce with high fidelity but occasionally give rise
to recombinants that also can replicate. Over the course of many
“generations†of selective amplification, novel variants arise and
grow to dominate the population based on their relative fitness under
the chosen reaction conditions. This is the first example, outside of
biology, of evolutionary adaptation in a molecular genetic system.
ttp://symposium.cshlp.org/content/early/2009/08/06/sqb.2009.74.004.a...
Departments of Chemistry and Molecular Biology and The Skaggs
Institute for Chemical Biology, The Scripps Research Institute, 10550
North Torrey Pines Road, La Jolla, CA 92037
Contributed by Gerald F. Joyce
A self-replicating molecule directs the covalent assembly of component
molecules to form a
product that is of identical composition to the parent. When the newly
formed product also is able to direct the assembly of product
molecules, the self-replicating system can be termed autocatalytic. A
self-replicating system was developed based on a ribozyme that
catalyzes the assembly of additional copies of itself through an RNA-
catalyzed RNA ligation reaction. The R3C ligase ribozyme was
redesigned so that it would ligate two substrates to generate an exact
copy of itself, which then would behave in a similar manner. This self-
replicating system depends on the catalytic nature of the RNA for the
generation of copies. A linear dependence was observed between the
initial rate of formation of new copies and the starting concentration
of ribozyme, consistent with exponential growth. The autocatalytic
rate constant was 0.011 min−1, whereas the
initial rate of reaction in the absence of pre-existing ribozyme was
only 3.3 × 10−11 M⋅min−1. Exponential growth was limited, however,
because newly formed ribozyme molecules had greater difficulty forming
a productive complex with the two substrates. Further optimization of
the system may lead to the sustained exponential growth of ribozymes
that undergo self-replication.
http://www.pnas.org/content/99/20/12733.abstract
Matthew Levy and Andrew D. Ellington*
+ Author Affiliations
Department of Chemistry and Biochemistry, Institute for Cell and
Molecular Biology, University of Texas, Austin, TX 78712
Edited by Gerald F. Joyce, The Scripps Research Institute, La Jolla,
CA, and approved April 10, 2003 (received for review January 9, 2003)
We have designed an autocatalytic cycle based on the highly efficient
10–23 RNA-cleaving deoxyribozyme that is capable of exponential
amplification of catalysis. In this system, complementary 10–23
variants were inactivated by circularization, creating
deoxyribozymogens. Upon linearization, the enzymes can act on their
complements, creating a cascade in which linearized species accumulate
exponentially. Seeding the system with a pool of linear catalysts
resulted not only in amplification of function but in sequence
selection and represents an in vitro selection experiment conducted in
the absence of any protein enzymes.
Self-Sustained Replication of an RNA Enzyme
Tracey A. Lincoln and Gerald F. Joyce*
The dawn of the RNA World: Toward functional complexity through
ligation of random RNA oligomers
Carlos Briones, Michael Stich and Susanna C. Manrubia
+ Author Affiliations
Centro de AstrobiologÃa (CSIC-INTA), 28850 Torrejón de Ardoz, Madrid,
Spain
A main unsolved problem in the RNA World scenario for the origin of
life is how a template-dependent RNA polymerase ribozyme emerged from
short RNA oligomers obtained by random polymerization on mineral
surfaces. A number of computational studies have shown that the
structural repertoire yielded by that process is dominated by
topologically simple structures, notably hairpin-like ones. A fraction
of these could display RNA ligase activity and catalyze the assembly
of larger, eventually functional RNA molecules retaining their
previous modular structure: molecular complexity increases but
template replication is absent. This allows us to build up a stepwise
model of ligation-based, modular evolution that could pave the way to
the emergence of a ribozyme with RNA replicase activity, step at which
information-driven Darwinian evolution would be triggered.
http://rnajournal.cshlp.org/content/15/5/743.abstract
An RNA enzyme that catalyzes the RNA-templated joining of RNA was
converted to a format whereby two enzymes catalyze each other's
synthesis from a total of four oligonucleotide substrates. These
cross- replicating RNA enzymes undergo self-sustained exponential
amplification in the absence of proteins or other biological
materials. Amplification occurs with a doubling time of about 1 hour
and can be continued indefinitely. Populations of various cross-
replicating enzymes were constructed and allowed to compete for a
common pool of substrates, during which recombinant replicators arose
and grew to dominate the population. These replicating RNA enzymes can
serve as an experimental model of a genetic system. Many such model
systems could be constructed, allowing different selective outcomes to
be related to the underlying properties of the genetic system.
Department of Chemistry, Department of Molecular Biology, and the
Skaggs Institute for Chemical Biology, The Scripps Research
Institute,
La Jolla, CA 92037, USA.
Szosak lab er nået vældigt langt på den måde, at man har konstrueret
cellemembraner, så er gennemtrængelige for aminosyrer, RNA osv. Derved
ar det lykkedes at supportere præcist, hvad der er formuleret omkring
den eukaryote celles organeller.
Her er en fin animation, som viser tingene og man kan læse videre på
siden om resultaterne af arbejdet;
http://genetics.mgh.harvard.edu/szostakweb/movies.html
> --
> Per Erik Rønne
http://www.RQNNE.dk
> Errare humanum est, sed in errore perseverare turpe