05-04-2003, 06:17 PM
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#62
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Veteran Member
Join Date: Mar 2001
Location: PA USA
Posts: 5,039
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Re: Yet another abiogensis thread for yguy
Last Week's Science News contained an article entitled "A Rocky Start.
http://www.sciencenews.org/20030426/bob10ref.asp
Some excerpts
Quote:
Like the age-old chicken-and-egg question, the source of the first cell membrane has been a major hurdle for the theories about the origin of life. Today's cell membranes are made of long, oily, lipid molecules that form into pliant fluidlike films surrounding a cell's biomolecular machinery. Such walls concentrate the molecules of life into a small space in which they can work together. "Without a membrane, a cell bleeds to death," Russell says.
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Lipid membranes may have self-assembled on the early Earth, acknowledge Martin and Russell. However, they question how those first lipid droplets could have contained precisely the right mix of ingredients for life. Perhaps more importantly, they ask, how would such protocells capture the energy required to create more of themselves?
"It's a huge stumbling block," Deamer agrees.
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The rock compartments nestled within the hydrothermal chimneys provide a possible answer. When rock membranes form in the laboratory, they create a voltage of 600 millivolts as their thin walls separate the simulated hydrothermal and ocean solutions, which have different ion concentrations. The voltage lasts for several hours, says Russell, and is comparable to that across the membranes of today's living cells.
"That energy would be sufficient to drive a putative metabolism," Russell notes.
Deamer remains skeptical, but he's intrigued enough that he's planning to conduct laboratory tests of his own to see whether iron sulfide structures can sustain voltages sufficient for catalyzing reactions that help form, for example, ATP—the cell's biochemical fuel.
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If Russell and Martin's theory has any chance of being right, naked, rock-cradled life-forms must at some point have invented the biochemistry required to produce their own membranes.
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Actually, Russell and Martin say, this crucial evolutionary leap may have happened in two different ways that correspond to what subsequently became archaebacteria and eubacteria.
Actually, Russell and Martin say, this crucial evolutionary leap may have happened in two different ways that correspond to what subsequently became archaebacteria and eubacteria.
The lipid molecules that build into the membranes of archaebacteria and eubacteria bear a subtle difference: One is the mirror image of the other. Although the difference between the forms carries no known consequence in terms of survival, it has major implications for the membranes' origins, says Yosuke Koga of the University of Occupational and Environmental Health in Kitakyushu, Japan.
Koga and his colleagues examined the genetic makeup of the key enzyme—(G-1-P) dehydrogenase—responsible for the formation of archaebacterial lipids. In 1998, the group reported that the genetic sequence encoding this membrane-building enzyme bore no resemblance to the corresponding enzyme in Escherichia coli, a representative eubacterium.
This genetic difference is too gaping for one type of membrane biochemistry to have evolved from the other, Koga argues. Therefore, he says, the two membrane types must have arisen independently, back when the first living cells emerged.
Martin and Russell conjecture that the bacterial ancestors living within their rock shelters cooked up two separate biochemical recipes for membranes. Then, with their distinctive membranes, the two types of cells presumably left their rocky starting places to begin paving their own evolutionary ways (see below).
For people hoping to find life on other planets, the iron sulfide theory's version of earthly events should come as good news. The environment that Russell and Martin propose as the birthplace of life requires only rocks, water, and the most basic of chemical ingredients. Given that there likely are billions of venues like that throughout the universe, says Russell, "life can't help but happen."
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I'd never read this angle before. I found it interesting.
The entire article is much more interesting but you have to be subscriber.
joe
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