Chemical experiments suggest the inevitability of organic life
Cyril Ponnamperuma looks at an oak tree and thinks of ``E.T.'' -- the extraterrestrial. The University of Maryland biochemist is trying to understand the origin of organic life. And the more his laboratory studies how life's fundamental chemical processes might arise, the more they seem to reflect the action of universal principles.
``As a matter of fact,'' he says, ``one might say that the universe is in the business of making life. All the [basic] processes seem to lead to that.'' He notes that, whether biochemists look at a microbe or an oak tree, they end up with two classes of large molecules as the chemical basis of earthly life. There are nucleic acids, such as DNA, which contain an organism's genetic blueprint. Then there are proteins, which carry out the chemical functions those genetic instructions specify.
In the university's Laboratory of Chemical Evolution, which he heads, Ponnamperuma and various research teams have been making the constituents of these basic molecules under simulated primordial conditions. Other scientists have carried out similar experiments for over three decades. The Maryland work, however, is not aimed simply at showing that these chemicals arise in an atmosphere rich in ammonia and methane, as might have existed on the early Earth. It's trying to understand why these chemical combinations, which make organic life work, form so readily when ``primordial'' material is energized by sparks (to simulate lightning).
In other words, is there a tendency in the underlying atomic snd molecular forces that favors the chemistry of life? In commenting on recent work of his laboratory at the annual meeting of the American Chemical Society last week, Ponnamperuma said he thinks there may well be such a fundamental cosmic bias.
Proteins consist of different combinations of 20 kinds of building blocks called amino acids. Five kinds of chemical units of a type known as ``bases,'' plus two kinds of sugar and a phosphate, go together in different ways to make nucleic acids. To use Ponnamperuma's metaphor, it's an ``alphabet'' of 28 letters with which to write the entire book of organic life.
It's these ``letters'' that are produced in the primordial experiments. Now the Maryland laboratory is trying to understand how this scheme and the genetic system it involves has arisen.
The instructions that specify the form and functions of an organism are encoded in the sequence of bases that make up DNA molecules. These instructions, in turn, control precisely how various amino acids are to be linked together to make specific proteins.
Ponnamperuma says he doubts that this finely tuned system developed by chance in a hit-or-miss evolutionary process. Recent experiments have shown that the ability of a given genetic instruction to specify which amino acid is to be put into a protein is a favored chemical process. It involves the least amount of energy of any of the possible chemical interactions that could occur. To a chemist, that means the working of the genetic code is as favored as is the tendency of water to run downhill.
This bias in favor of the chemistry of organic life may start with the elements themselves. Ponnamperuma notes that the most abundant elements -- the elements which nature makes most easily -- are hydrogen, nitrogen, oxygen, and carbon. These are the elements that readily combine to form the 28 letters of life's alphabet. And these amino acids, bases, sugars, and phosphate also readily combine into nucleic acids and proteins. All of this leads Ponnamperuma to think that there is a bias toward organic life in the basic chemical forces. He says that this, in turn, suggests that, if there is life elsewhere, it's likely to be similar, chemically speaking, to life on Earth.
It's a big jump from such speculation to conclude that ``E.T.'' really exists. There's no scientific evidence about extraterrestrial life one way or the other. However, the work of the Maryland laboratory and Ponnamperuma's conclusions from that work do suggest that life as we know it on Earth is no accident.
A Tuesday column. Robert C. Cowen is the Monitor's natural science editor.