Clue to life's cellular origins.

Clues to life's cellular origins

A discovery by a biophysicist at the University of California at Davis indicates that the structural requirements for cell membranes should have been present in earth's primordial soup. David W. Deamer has found that in the interior of the 4.5-billion-year-old Murchison meteorite are lipid-like organic chemicals able to self-assemble into a membrane-like film enclosing fluid. The finding was presented last week in Berkeley, Calif., at a meeting of the International Society for the Study of Origins of Life.

"If we assume life begins from self-assembly," Deamer says, "then the non-biological self-assembly seen with chemicals from inside the Murchison meteorite shows how the essential membrane of the first microorganism might have formed." Such a mebrane, notes Cyril Ponnamperuma at the University of Maryland in College Park, "is required in order to get a cell." What Deamer's work shows, he says, "is that the materials required for a membrane will be available."

The Murchison meteorite gets its name from the site in Australia where it fell to earth in 1969. It is believed to have broken off of an asteroid that formed at about the same time and from some of the same solar-system materials that earth did.

Ponnamperuma says his own work with Murchison-derived chemicals provided "the first unambiguous evidence of extraterrestrial amino acids" and, more recently, the presence of all five nucliec acid bases (SN:9/3/83, p. 150). He says that if Deamer's work can be substantiated further, chemical-origins-of-life proponents will be one step closer to establishing that the material in the Murchison meteorite -- and therefore elsewhere in the solar system -- contains many of the essential components for creating life.

However, Deamer cautions, "there is no evidence that these [membranous structures formed from Murchison chemicals] were in the direct line of ascendancy for the life that actually did form on earth." In fact, he notes, the chemical composition of the Murchison compounds he discovered has not yet been characterized except for the observation that they are lipid-like and fluorescent and contain unique complex-hydrocarbon compounds.

Deamer says that if chemicals like those in the Murchison interior were not naturally available on the primordial earth, they could have been "seeded" into the chemical soup from which life is believed to have formed, by similar chemicals arriving with earlier Murchison-like meteors.