Ugly Bags of Mostly Water
The Life of a Lab Rat blog reported this week on a new experimental study demonstrating that fatty acid vesicles – essentially the stuff one makes a cell membrane out of – can survive at much higher temperatures than previously suspected; up to 100º C.
This is good news for emergence of life (EOL) research. A major working hypothesis in EOL research maintains that life began as complexes of self-assembling RNA curlicues in hot water, probably in hydrothermal vent systems on the ocean floor. These settings are optimal for abiogenesis, for a variety of reasons, but a nagging problem has been the transition from trapped RNA proto-replicators in vent plumbing to free-floating cells. Hydrothermal vents are underlain by massive, convoluted networks of cracks, fissures, conduits, manifolds, and vugs through which volcanic mineral-laden water and gas flow. Backwater cavities and chambers in the plumbing are nice places to cook up little self-contained bioreactors for RNA self-replication, but how do you get that stuff to move out of the house?
Micelles are the easiest way; add a phosphate to a lipid chain and you can make a fatty acid capable of self-assembling into a micelle, the first step on the path to the robust phospholipid bilayer enclosing all cells today. Micelles can contain water and nutrients and can be semi-permeable. They’re good workhorses for carrying the machinery of life from place to place, even though they’re basically just plastic bags. Micelles tend to degenerate at higher temperatures in water, but a new study by S. S. Mansy and J. W. Szostak (Scripps Research Institute) demonstrates that micelles can be stable up to 100º C. At such temperatures, DNA inside micelles can separate into strands, and then recombine again at lower temperatures, all within an intact micelle. Unzipping and re-zipping DNA is a core process in cell replication, so this study closes one more gap in our knowledge of how simple chemicals self-organized on the Hadean Earth to form the earliest forms of life.