domingo, 25 de septiembre de 2011
Did Life on Earth Emerge from Non-organic Matter?
How did life on Earth begin? An giant step toward solving this puzzle was taken in the 1980's with the Nobel Prize–winning discovery by Tom Cech and Sidney Altman that RNA, the sister molecule of DNA, can catalyze certain chemical reactions inside cells, a job previously thought to be the exclusive domain of proteins. Until their discovery, RNA was thought to have just one function: storing the genetic information cells need to build proteins.
This new revelation about RNA's dual role suggested to some scientists, including Harvard's Jack Szostak, that RNA likely existed long before DNA or proteins because it might be able to catalyze its own reproduction. Their discovery made it easier to think about how life began, Szostak says.
"They inspired me to try to think of ways to make RNAs in the lab that could catalyze their own replication."
Szostak and his team is working to recreate a hypothetical model of this process in the laboratory. By building simple cell-like structures in a test tube, they are attempting to establish a plausible path that led primitive cells to emerge from simple chemicals. Ultimately, Szostak hopes to answer fundamental questions about evolution's earliest steps.
Building on earlier work by other scientists, Szostak and colleagues began experimenting with a clay mixture common on early Earth called montmorillonite, which was found to catalyze the chemical reactions needed to make RNA.
So, did life originally spring from clay as some creation myths assert? Not necessarily, but it does provide a possible mechanism for explaining how life initially arose from nonliving molecules. Szostak's team at the Howard Hughes Medical Institute and Massachusetts General Hospital showed that the presence of clay aids naturally occurring reactions that result in the formation of fatty sacks called vesicles, similar to what scientists expect the first living cells to have looked like. Further, the clay helps RNA form. The RNA can stick to the clay and move with it into the vesicles. This provides a method for RNA's critical genetic information to move inside a primitive cell.
"It's exciting because we know that a particular clay mineral helps with the assembly of RNA," Szostak said. "There certainly would have been lots of environments on early Earth with clay minerals. It's something that forms relatively easily as rocks weather."
The researchers also found that the clay expedited the process by which fatty acids form vesicles that could serve as cell membranes. When RNA and fatty acids were mixed with the montmorillonite, the clay seemed to help transport the RNA inside the vesicles, forming a cell-like structure. Szostak and his team surmised that a similar process could possibly have led to the creation of the first cell.
The Daily Galaxy