Evolutionary Biology Lecture of the Week: Less Tar, More Life
- From: Wirt Atmar <atmar@xxxxxxxxxxxxxxxxx>
- Date: Mon, 10 Apr 2006 11:45:36 -0400 (EDT)
Ladies and Gentlemen:
The Evolutionary Biology Lecture of the Week for April 10, 2006 is now
available at:
http://aics-research.com/lotw/
The talks center primarily around evolutionary biology, in all of its
aspects: cosmology, astronomy, planetology, geology, astrobiology,
ecology, ethology, biogeography, phylogenetics and evolutionary biology
itself, and are presented at a professional level, that of one scientist
talking to another. All of the talks were recorded live at conferences.
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April 10, 2006
Less Tar, More Life
Constraining Scenarios for the Origin of Life: Working Backwards,
Working Forwards, and Synthesizing Life in the Laboratory
Steven Benner, University of Florida
27 min. (requires QCShow Player)
Sugars are the literal backbone of life on this planet. In particular,
one rare form of sugar, ribose, is the structural spine of RNA and DNA.
Evidence for an "RNA world," an hypothesized episode of the earliest
form of life on Earth during which RNA was the only genetically encoded
component of biological catalysts, is found in the ribosome, in
catalytic RNA molecules, and in contemporary metabolisms. Nonetheless,
for all of its importance, the fact that RNA could form spontaneously
and persist under prebiotic conditions has been seriously doubted.
In 1953, Stanley Miller demonstrated that electric sparks in a primitive
atmosphere made amino acids, the building blocks of proteins. Miller's
experiment however failed to identify sugars that were needed for
genetic material. Steven Benner, this week's lecturer, has said, "The
sugar ribose can be formed from interstellar precursors under prebiotic
conditions, but ribose is too unstable to survive under Miller's
conditions." It turns into tar if not handled very carefully.
Miller's discouragement, after 40 years of experiments in trying to
synthesize ribose prebiotically, was such that it caused him to write in
1995, "The first genetic material could not have contained ribose or
other sugars because of their instability."
In contrast, Benner offers in this talk a very simple mechanism to allow
the prebiotic formation and persistence of ribose. The presence of
boron, which is derived from borate minerals, allows ribose and other
sugars to remain stable for days.
Borates are not rare on planetary surfaces. Borate is incompatible with
many silicate minerals, and because of that incompatability is
concentrated in residual melts during rock formation, and frequently
appears in igneous rocks as tourmalines. Weathering produces soluble
borate salts, which often appear as alkaline evaporites. They are known
in Death Valley, and they appear as crusts on outcrops in Antarctic dry
valleys, and are likely on the surface of Mars as well.
While Benner is not claiming that this is the precise path that the
initial evolution of life on this planet took, it makes its likelihood
enormously more plausible and all the more simple.
In the second half of the talk, Benner changes gears and speaks to the
subject of the artificial synthesis of life in the laboratory. At the
core of all life on Earth lies an alphabet of five bases, A, G, C, T and
U. These are the base pairs that interlock the ribose spine in the
information-bearing molecules, RNA and DNA.
Benner notes that there is no reason to suspect that these five bases
were the only bases used in the earliest forms of life. He outlines
eight more bases that fit the necessary Watson-Crick geometry and
presents a logical argument that these other bases ? or something very
much like them ? quite likely existed in the first forms of RNA on Earth.
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