US chemists at the University of Georgia have for the first time showed how simple molecules can combine chemically rather than biologically to form the building blocks of DNA, the key component of all life forms on Earth.
In experiments they showed how a combination of five cyanide molecules could build up adenine, one of the four building blocks of DNA.
"Just where these biomolecules originated isn't known. 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," said Paul von Ragué Schleyer, Graham Perdue Professor of Chemistry at the University of Georgia.
Schleyer said the scientists focused on adenine because of its relative prevalence on Earth and its formation in the dark in from simple components.
He said along with other fundamental building blocks, adenine has also been detected extra-terrestrially. However, the vast distance between the smaller molecules required to form adenine in outer space precluded its formation, unless some nucleation centres, like specks of interstellar dust, were present, he said.
"Numerous experiments have demonstrated that amino acids, nucleotides, carbohydrates and other essential compounds form under simulated primitive Earth conditions. Remarkably, a solution of highly poisonous cyanide in ammonia, frozen solid in a refrigerator for 25 years, produced adenine, a necessary component of life," Schleyer and his team wrote in their study.
"A substantial amount of adenine was also formed in a high-temperature experiment designed to simulate early volcano-like environments. But the question is how," the study said.
The research appears in the current print issue of the Proceedings of the National Academies of Science (PNAS).