How did chemical constituents essential to life arise on primitive Earth?

Experiments show that simple molecules can combine chemically rather than biologically to form the building blocks of DNA, the key component of all life forms. These processes might have taken place on primitive earth, but how they occur is an unsolved puzzle.

Chemists at the University of Georgia have now proposed the first detailed, feasible mechanism to explain how adenine, one of the four building blocks of DNA, might be built up from the combination of five cyanide molecules. The investigation is based on extensive quantum chemical computations over several years.

“Just where these biomolecules originated isn’t known,” said Paul von Ragué Schleyer, Graham Perdue Professor of Chemistry at the University of Georgia. “One can only speculate. They could have formed from smaller molecules present on primitive Earth, either very slowly over millions of years or rapidly before the Earth cooled down. Asteroids may have brought them from outer space, but how did biomolecules form there?”

The newly proposed mechanism for the formation of adenine gives a clear picture of how it could have become one of the building blocks essential for the formation of DNA. The research was published today in the print version of the Proceedings of the National Academies of Science. Schleyer’s coworkers were Ph. D. candidate Debjani Roy, the first author of the paper, and Katayoun Najafian, his former student from Iran.

DNA is the nucleic acid blueprint of life that is passed on from generation to generation. First isolated in 1869 from the pus of discarded surgical bandages by Friedrich Miescher, a Swiss doctor, DNA’s double helix structure was solved by Watson and Crick in 1953. DNA is shaped somewhat like a twisted ladder with the rungs anchored by matching pairs of only four bases: adenine, guanine, cytosine and thymine.

The UGA chemists focused on adenine because of its relative prevalence on Earth and its formation in the dark in from simple components. Along with other fundamental building blocks, adenine has even been detected extraterrestrially. Still, the vast distance between the smaller molecules required to form adenine in outer space precludes its formation, unless some nucleation centers, like specks of interstellar dust, are present.

“Numerous experiments have demonstrated that amino acids, nucleotides, carbohydrates and other essential compounds form under simulated primitive Earth conditions,” the authors write in their paper.

Remarkably, a solution of highly poisonous cyanide in ammonia, frozen solid in a refrigerator for 25 years, produced adenine, a necessary component of life. A substantial amount of adenine also was formed in a high-temperature experiment designed to simulate early volcano-like environments. But the question is how.

The Georgia researchers arrived at an answer by solving a series of key riddles. They worked out the processes in which five cyanide molecules might combine to form adenine under terrestrial conditions. Their predictions are based on extensive computations of sequences of reaction steps along possible mechanistic routes.

“Finding a viable, thermodynamically feasible, step-by-step mechanism that can account for the formation of adenine was far from straightforward,” the authors said. “Our report provides a more detailed understanding of some of the chemical process involved in chemical evolution, and a partial answer to the fundamental question of molecular biogenesis. Our investigation should trigger similar investigations of the abiotic formation of the remaining nucleic acid bases as well as other biologically relevant molecules.”

Source: University of Georgia

Related stories:

Enzyme complex could be key to new cancer treatments
Penn State scientists are the first to observe in living cells a key step in the creation of adenine and guanine, two of the four building blocks that comprise DNA. Also called purines, the two building blocks are essential for cell replication. The findings, which will be published in the 4 April 2008 issue of the journal Science, could lead to new cancer treatments that prevent cancer cells from replicating by interfering with their abilities to make purines.
Researchers make first direct observation of 3-D molecule folding in real time
All the crucial proteins in our bodies must fold into complex shapes to do their jobs. These snarled molecules grip other molecules to move them around, to speed up important chemical reactions or to grab onto our genes, turning them "on" and "off" to affect which proteins our cells make.
Researcher presents origin-of-life theory for young Earth, supports life on other planets
Some of the elements necessary to support life on Earth are widely known – oxygen, carbon and water, to name a few. Just as important in the existence of life as any other component is the presence of adenine, an essential organic molecule. Without it, the basic building blocks of life would not come together. Scientists have been trying to find the origin of Earth’s adenine and where else it might exist in the solar system. University of Missouri-Columbia researcher Rainer Glaser may have the answer.
Researcher Presents Origin-Of-Life Theory for Young Earth
Some of the elements necessary to support life on Earth are widely known - oxygen, carbon and water, to name a few. Just as important in the existence of life as any other component is the presence of adenine, an essential organic molecule. Without it, the basic building blocks of life would not come together.
Nobel Laureate finds 'elegant' explanation for DNA transcribing enzyme's high fidelity
Last month, Roger Kornberg of Stanford University won the Nobel Prize in Chemistry for his efforts to unravel the molecular basis of eukaryotic transcription, in which enzymes give “voice” to DNA by copying it into the RNA molecules that serve as templates for protein in organisms from yeast to humans. Now, Kornberg and his colleagues report in the December 1, 2006 issue of the journal Cell, published by Cell Press, new structures that reveal another critical piece of the puzzle: how the so-called polymerase II enzyme discriminates among potential RNA building blocks to ensure the characteristic accuracy of the process.
Origin of life: the search for the first genetic material
How did life originate on Earth? Until now, there have only been theories to answer this question. One of the fundamental steps leading to living organisms is the development of molecules that can replicate and multiply themselves—the first genetic material. A team led by Ramanarayanan Krishnamurthy and Albert Eschenmoser at The Scripps Research Institute in La Jolla, California, is researching how this molecule might have looked.
Ingredients for DNA and Protein Found Around Star
NASA's Spitzer Space Telescope has discovered some of life's most basic ingredients in the dust swirling around a young star. The ingredients - gaseous precursors to DNA and protein - were detected in the star's terrestrial planet zone, a region where rocky planets such as Earth are thought to be born.
Biological electron transfer captured in real time
Two research teams led by Dr. Michael Verkhovsky and Prof. Mårten Wikström of the Institute of Biotechnology of the University of Helsinki have for the first time succeeded in monitoring electron transfer by Complex I in real time. In the future, this work might, for example, have medical relevance, because most of the maternally inherited so-called mitochondrial diseases are caused by dysfunction of Complex I.

News discussion:

General Science news