A question that has plagued scientists for a long time is
centered around the question as to how life began on planet earth. It is well known that life is found even
under the most inhospitable conditions – a stunning example of this is that life
exists within the deep sea hydrothermal vents that are found on the ocean floor. In addition, microorganisms such as
Hormoconis resinae contaminate jet fuel – using this hydrocarbon source as a
vital nutrient – and are known to cause corrosion in the tanks that hold this
fuel.
Therefore, it can be reasonably postulated that simple life
forms could thrive in the harsh conditions of prebiotic earth when oxygen was
not present within the atmosphere at that time.
But the question remains as to how did life begin – what was the process
by which self-sustaining living organisms were formed from rudimentary compounds.
It has been shown that in an artificial environment created
in the laboratory in which an
atmospheric environment was created to simulate the conditions believed to have
existed in the prebiotic world, the addition of an energy source – such as
lightening – produced rudimentary organic compounds found in living cells. These experiments were conducted in the
1950's, by the biochemists Stanley Miller and Harold Urey. These results are only suggestive evidence
that organic compounds could have been created spontaneously in the early-earth
environment. It is, of course, far from
the complete story.
Since DNA and RNA are fundamental ingredients to all of life
as we know it and capable of self-replication, a key step in the evolution of
life would be the conversion of simple organic compounds to purines that are
some of the important building blocks for both DNA and RNA and for the
synthesis of Adenosine Triphosphate (ATP) – the molecule that is responsible
for trapping energy derived from metabolism for all of life.
Furthermore, the preponderance of evidence now suggests that
RNA may have preceded DNA as the repository of genetic information capable of
self-replication. Certain forms of RNA
also demonstrate catalytic properties (ribozymes) that are essential to sustain
life. Of course, contemporary advanced
cell structure uses a host of enzymes to accomplish essential catalytic
functions.
RNA is made of four different nucleobases -two pyrimidines – cytosine and uracil – and two
purines adenine and guanine. Previous
work done by John D. Sutherland from the School of Chemistry, University of
Manchester, UK has shown a plausible synthetic route to pyrimidines in an
abiotic environment. But the route to
purines has been more elusive.
Recent work by T. Carell from the Department of Chemistry,
Ludwig-Maximilians University Munich, Germany and fellow investigators has
recently demonstrated a mechanism that could account for spontaneous creation
of purines from simpler compounds readily available within the natural environment
of early earth. The pathway involves the
spontaneous synthesis of aminopyrimidines from hydrogen, cyanide and water –
compounds readily available in the early earth environment. Although aminopyrimidines can produce a wide range
of synthetic products, in an environment of formic acid, the predominant
product is formamidopyrimidine (FaPy) known to readily produce purines. Furthermore, formic acid has been shown to be
present in comets that collided frequently with earth during the early stages
of its evolution.
Formamidopyrimidine
Although this work is very significant, it does not explain
how purines and pyrimidines would lead to the creation of more complex and
sophisticated RNA molecules. Nor does it
shed any real light on the requisite formation of a cellular environment for biosynthetic
reactions so necessary for the containment and sustenance of life processes.
