How did we go from a lifeless Earth with no oxygen to a planet teeming with life and that essential element? Scientists at the Georgia Institute of Technology have found one crucial clue: iron and RNA.
The team managed to re-create conditions of life on Earth 3 billion years ago and"revived" a function of RNA that may have subsided after the rise of DNA.
Life as we know it depends on the precise interplay of DNA, the double-helix molecular structure that safeguards genetic code, with RNA and proteins. But many scientists -- among them Francis Crick, who, with James Watson, discovered DNA -- have theorized that early life could have relied on RNA alone. The debate has been a chicken-and-egg affair for decades.
Researchers swayed by the RNA-first theory are intrigued by ribozymes, a type of RNA, discovered in the 1980s, that acts as an enzyme -- a role once thought to be exclusive to proteins. Its discovery was the beginning of a shift in the view that RNA was mostly a temporary replica of DNA that acted as a "messenger" to transfers genetic code. RNA's mysterious shape-shifting and complicated role has further increased scientists' curiosity about its evolution.
Scientists think ribozymes may hint at an archaic process that once was the king-maker of life. They have been trying to see how RNA behaved at a time when Earth's composition was much different -- no oxygen and abundant iron was the rule of the day 3 billion years ago.
The Georgia Tech team last year proposed that RNA could have been catalyzing chemical processes vital to life by utilizing an ion of iron in an oxygen-free environment. Magnesium ions serve that purpose in the modern, oxygen-rich world.
Using a select set of RNA molecules in the absence of oxygen, the researchers observed this catalysis – an electron was transferred. The same process failed to occur with magnesium ions.
"Our study shows that when RNA teams up with iron in an oxygen-free environment, RNA displays the powerful ability to catalyze single electron transfer, a process involved in the most sophisticated biochemistry, yet previously uncharacterized for RNA," said Loren Williams, a Georgia Tech biochemist.