How a key component of DNA formed on the early Earth

Abiogenesis – theories about how life first living from non-living chemicals – is an enduring scientific puzzle. Theories abound, but deciding among them is difficult because of the limited evidence on conditions in the early earth, and the difficulty of recreating these conditions in the laboratory (in particular, it is thought that the conditions for abiogenesis took millions of years to develop).

But an important part of the puzzle has been solved in a paper published today. Adenine, a key constituent of DNA, is known to form spontaneuosly from more basic building blocks. Famously, in 1953, Stanley Miller conducted a simple experiment that showed adenine could be created in a stormy atmosphere of volcanic gases (although he was wrong about the composition of the early atmosphere. Later experiments showed that adenine could form from an aqueous solution of ammonia and cyanide. In 2006, Stanley Miller and colleagues demonstrated a new pathway, this time under frozen conditions.

The results of these experiments is an embarrasement of riches: the problem in 2007 is not could adenine form spontaneously, but rather how did it form? That’s where the new paper by Debjani Roy and colleagues comes in. They used computational chemistry (i.e. simulating a vast array of chemical reactions) to show that certain pathways, specifically those involving water or ammonia, are much faster and easier than others. Step by step, the process by which life formed on the early earth are being revealed.

Refs:

James Cleaves II et al. The prebiotic synthesis of pyrimidines in frozen solution. Naturwissenschaften 2006; 93: 228-231.
Roy et al. Chemical evolution: The mechanism of the formation of adenine under prebiotic conditions. PNAS 2007;104 : 17272-17277