Replicação de DNA... sem vida

sexta-feira, maio 28, 2010

DNA replication... without life

27 May 2010 by Kate McAlpine

Magazine issue 2762.

THE precursor of life may have learned how to copy itself thanks to simple convection at the bottom of the ocean. Lab experiments reveal how DNA replication could have occurred in tiny pores around undersea vents.

One of the initial steps towards life was the first molecule capable of copying itself. In the open ocean of early Earth, strands of DNA and loose nucleotides would have been too diluted for replication to occur. So how did they do it?

Providing a perfect setting for life to replicate (Image: University of Delaware/JGI/DOE)

Inside many undersea hydrothermal vents, magnesium-rich rocks react with sea water. Such reactions create a heat source that could drive miniature convection currents in nearby pores in the rock, claim Christof Mast and Dieter Braun of Ludwig Maximilian University of Munich, Germany. They propose that such convection could concentrate nucleotides, strands of DNA, and polymerase, providing a setting that would promote replication.

Sea water inside pores on or near a vent's chimney may undergo thermal convection because the water at the wall of the pore closest to the vent's heat source would be warmer than the water near the furthermost wall, say Mast and Braun. If the pore contained strands of DNA, nucleotides, and polymerase they would ride upward in the warm current. The DNA strands would also be "unzipped" in the heat, splitting into two strands that each serve as templates for eventual replication.


Read more here/Leia mais aqui: New Scientist


Artigos citados no texto da New Scientist:

1. Phys. Rev. Lett. 104, 188102 (2010) [4 pages]

Thermal Trap for DNA Replication

Christof B. Mast and Dieter Braun*
Systems Biophysics, Physics Department, Center for Nanoscience, Ludwig Maximilians Universität München, Amalienstrasse 54, 80799 München, Germany

Received 1 August 2009; published 7 May 2010

The hallmark of living matter is the replication of genetic molecules and their active storage against diffusion. We implement both in the simple nonequilibrium environment of a temperature gradient. Convective flow both drives the DNA replicating polymerase chain reaction while concurrent thermophoresis accumulates the replicated 143 base pair DNA in bulk solution. The time constant for accumulation is 92 s while DNA is doubled every 50 s. The experiments explore conditions in pores of hydrothermal rock which can serve as a model environment for the origin of life.

© 2010 The American Physical Society
87.14.gk, 87.15.R-


2. Journal of the American Chemical Society

Formation of Protocell-like Vesicles in a Thermal Diffusion Column

Itay Budin†§, Raphael J. Bruckner‡§ and Jack W. Szostak*§

Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts 02138, Department of Genetics, Harvard Medical School, Boston, Massachusetts 02115, and Howard Hughes Medical Institute, Department of Molecular Biology, and Center for Computational and Integrative Biology, Massachusetts General Hospital, Boston, Massachusetts 02114

J. Am. Chem. Soc., 2009, 131 (28), pp 9628–9629
DOI: 10.1021/ja9029818
Publication Date (Web): June 24, 2009
Copyright © 2009 American Chemical Society, †

Harvard University., ‡ Harvard Medical School., § Massachusetts General Hospital


Many of the properties of bilayer membranes composed of simple single-chain amphiphiles seem to be well-suited for a potential role as primitive cell membranes. However, the spontaneous formation of membranes from such amphiphiles is a concentration-dependent process in which a significant critical aggregate concentration (cac) must be reached. Since most scenarios for the prebiotic synthesis of fatty acids and related amphiphiles would result in dilute solutions well below the cac, the identification of mechanisms that would lead to increased local amphiphile concentrations is an important aspect of defining reasonable conditions for the origin of cellular life. Narrow, vertically oriented channels within the mineral precipitates of hydrothermal vent towers have previously been proposed to act as natural Clusius−Dickel thermal diffusion columns, in which a strong transverse thermal gradient concentrates dilute molecules through the coupling of thermophoresis and convection. Here we experimentally demonstrate that a microcapillary acting as a thermal diffusion column can concentrate a solution of oleic acid. Upon concentration, self-assembly of large vesicles occurs in regions where the cac is exceeded. We detected vesicle formation by fluorescence microscopy of encapsulated dye cargoes, which simultaneously concentrated in our channels. Our findings suggest a novel means by which simple physical processes could have led to the spontaneous formation of cell-like structures from a dilute prebiotic reservoir.

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