Article: Scientists propose the kind of chemistry that led to life
- From: "Robert Karl Stonjek" <rstonjek@xxxxxxxxxxxxxx>
- Date: Sun, 10 Jun 2007 02:05:51 -0400 (EDT)
Scientists propose the kind of chemistry that led to life
Before life emerged on earth, either a primitive kind of metabolism or an
RNA-like duplicating machinery must have set the stage - so experts believe.
But what preceded these pre-life steps?
A pair of UCSF scientists has developed a model explaining how simple
chemical and physical processes may have laid the foundation for life. Like
all useful models, theirs can be tested, and they describe how this can be
done. Their model is based on simple, well-known chemical and physical laws.
The work appears online this week in The Proceedings of the National Academy
of Sciences.
The basic idea is that simple principles of chemical interactions allow for
a kind of natural selection on a micro scale: enzymes can cooperate and
compete with each other in simple ways, leading to arrangements that can
become stable, or "locked in," says Ken Dill, PhD, senior author of the
paper and professor of pharmaceutical chemistry at UCSF.
The scientists compare this chemical process of "search, selection, and
memory" to another well-studied process: different rates of neuron firing in
the brain lead to new connections between neurons and ultimately to the
mature wiring pattern of the brain. Similarly, social ants first search
randomly, then discover food, and finally build a short-term memory for the
entire colony using chemical trails.
They also compare the chemical steps to Darwin's principles of evolution:
random selection of traits in different organisms, selection of the most
adaptive traits, and then the inheritance of the traits best suited to the
environment (and presumably the disappearance of those with less adaptive
traits).
Like these more obvious processes, the chemical interactions in the model
involve competition, cooperation, innovation and a preference for
consistency, they say.
The model focuses on enzymes that function as catalysts - compounds that
greatly speed up a reaction without themselves being changed in the process.
Catalysts are very common in living systems as well as industrial processes.
Many researchers believe the first primitive catalysts on earth were nothing
more complicated than the surfaces of clays or other minerals.
In its simplest form, the model shows how two catalysts in a solution, A and
B, each acting to catalyze a different reaction, could end up forming what
the scientists call a complex, AB. The deciding factor is the relative
concentration of their desired partners. The process could go like this:
Catalyst A produces a chemical that catalyst B uses. Now, since B normally
seeks out this chemical, sometimes B will be attracted to A -- if its
desired chemical is not otherwise available nearby. As a result, A and B
will come into proximity, forming a complex.
The word "complex" is key because it shows how simple chemical interactions,
with few players, and following basic chemical laws, can lead to a novel
combination of molecules of greater complexity. The emergence of
complexity - whether in neuronal systems, social systems, or the evolution
of life, or of the entire universe -- has long been a major puzzle,
particularly in efforts to determine how life emerged.
Dill calls the chemical interactions "stochastic innovation" - suggesting
that it involves both random (stochastic) interactions and the emergence of
novel arrangements.
"A major question about life's origins is how chemicals, which have no
self-interest, became 'biological' -- driven to evolve by natural
selection," he says. "This simple model shows a plausible route to this
type of complexity." Dill is also a professor of biophysics and associate
dean of research in the UCSF School of Pharmacy. He is a faculty affiliate
at QB3, the California Institute for Quantitative Biomedical Research,
headquartered at UCSF.
Source: University of California - San Francisco
http://www.physorg.com/news100533246.html
Posted by
Robert Karl Stonjek
.
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