The Final Step(s)?

In a 2005 paper in Trends in Biotechnology, David Deamer presented 12 requirements to creating a protocell capitulates life. Then have ben accomplished in different labs and in different ways. Because researchers have used RNA as both a macromolecular catalyst and as an information store, some of the boundaries between objectives become blurred. That's one of the reasons that Deamer says once the 11th requirement is met and macromolecular catalysts are reproduced in the protocell during growth, the final hurdle, in which duplicating genetic information is passed between generations, will already have been achieved.

Illustration by Scott Bodell

In 1965 Alec Bangham and colleagues at the Agricultural Research Council Institute of Animal Physiology in Cambridge, England, describe research showing that amphiphilic molecules can self-assemble into microscopic sacs sharing some properties of cell membranes. ¹

Efraim Racker and Walther Stoeckenius of Cornell University in Ithica, NY, incorporated bacteriorhodopsins and an ATPase into a liposome membrane to generate ATP from light. ²

Several previous attempts had demonstrated liposomes capable of maintaining proton gradients. In 2004 Irene Chen and Jack Szostak of Massachusetts General Hospital found membrane growth could generate gradients lasting several hours. ³

In 1985, David Deamer and Roberta Shew of the University of California, Davis, report that macromolecules can easily be captured in lipid vesicles by mixing the vesicles with the molecules, then drying and rehydrating the mixture. ⁴

In 1994, Deamer and colleagues synthesize RNA in lipid vesicles by using a an RNA polymerase to string together molecules of adenosine diphosphate (ADP) that had been encapsulated within the compartments. ⁵

Though it hasn't been demonstrated inside a liposome, several groups have built in vitro evolution systems in which successive generations of RNA molecules evolve to more efficiently catalyze reactions such as ligating other RNAs. ⁶

Several groups have captured DNA molecules within liposomes to direct the production of proteins, including Green Fluorescent Protein, channel proteins, and polymerases, through transcription and translation. ⁷

In 2004, researchers at Osaka University, Japan, create a membrane-bound system containing a two-stage genetic cascade. DNA directs production of an RNA polymerase, which is required to produce Green Fluorescent Protein. ⁸

In 2003, researchers at Massachusetts General Hospital report that fatty acid vesicles grow by taking up additional available fatty acids, and divide when extruded through pores. ⁹

In 2001, David Bartel of the Massachusetts Institute of Technology and collagues report developing an RNA enzyme, or ribozyme, that catalyzes the replication of an RNA template molecule, making rare errors along the way. ¹⁰