HOW DID LIFE BEGIN?

In bubbles? On comets? Along ocean vents? Scientists find some 
surprising answers to the greatest mystery on earth.

By J. MADELEINE NASH/LA JOLLA

THE PRIMORDIAL CHEMISTRY LAB

Life's beginnings did not have the benefit of Miller's glass bottles, test
tubes and vials. So how did nature bring the right ingredients for life
together in an orderly fashion? One possibility recently suggested by Louis
Lerman, a researcher at Lawrence Berkeley Laboratory, is that bubbles in
the ocean served as miniature chemical reactors. Bubbles are ubiquitous,
Lerman notes; at any given time, 5% of the ocean surface is covered with
foam. In addition, bubbles tend to collect and concentrate many chemicals
essential to life, including such trace metals as copper and zinc and salts
like phosphate. Best of all, when bubbles burst, they forcibly eject their
accumulated molecules into the atmosphere, where other scientists feel the
most important chemistry takes place.

 Biologist Harold Morowitz of George Mason University in Fairfax, Virginia,
suspects that life arose in a less ephemeral chemistry lab than a bursting
bubble. He focuses on Janus-faced molecules found in nature called
amphiphiles. These molecules have one side with an affinity for water and
another side that is repelled by water. Bobbing in the primitive oceans,
the molecules would have hidden their water-hating sides away by curling
into tiny spheres. These spheres, known as vesicles, would have provided an
ideal setting for chemical reactions and could have been precursors to the
first cells. ``Once you have these little vesicles,'' says Morowitz,
``you're on the way to life.''

 Which came first, though, the membrane or the metabolism? Gunter
Wachtershauser, a patent attorney from Munich who also happens to be a
theoretical chemist, believes that what we call life began as a series of
chemical reactions between certain key organic molecules. Instead of being
enclosed in a membrane, he says, they might have been stuck like pins in a
cushion on the surface of some accommodating material. Wachtershauser's
surprising candidate for this all-important material: pyrite, or fool's
gold. Since the shiny crystal carries a positive electrical charge, it
could have attracted negatively charged organic molecules, bringing them
close enough to interact. Wachtershauser thinks these reactions could have
led to the development of something similar to photosynthesis.

 Still unanswered is the riddle of how these molecules came to reproduce.
Chemist A.G. Cairns-Smith of the University of Glasgow thinks the answer
may lie not in glittery fool's gold but in ordinary clay. The structure of
certain clays repeats the same crystalline pattern over and over again.
More important, when a defect occurs, it is repeated from then on, rather
like a mutation in a strand of DNA. While few scientists believe such
inorganic materials are actually alive, a number take very seriously the
idea that clay or mineral crystals could have served as molecular molds
that incorporated life's building blocks and organized them in precise
arrays.

MOLECULAR ANCESTORS

Even if one accepts the fact that organic molecules can spontaneously
organize themselves and, further, that these molecules might spontaneously
reproduce, there remains a fundamental chicken-and-egg problem. Modern
cells are made of proteins, and the blueprints for the proteins are
contained in long strands of DNA and RNA. But DNA and RNA cannot be
manufactured without an adequate supply of proteins, which act as catalysts
in the construction process. How, then, could nucleic acids get started
without proteins, or vice versa?

 One solution was put forward a decade ago, when researchers discovered
that certain RNA molecules can act both as blueprints and catalysts,
stimulating reactions between themselves and other molecules. Up to that
point, scientists had thought of RNAs as merely molecular messengers
carrying genetic instructions from DNA to the cell's protein factories.
Suddenly RNA was seen in a totally different light. If RNA could catalyze
reactions, perhaps at some point in the past, it spurred its own
replication. Then it could have been much more than DNA's intermediary: it
could have been DNA's ancestor. According to this line of reasoning, the
first organisms lived in an `` RNA world,'' and DNA did not develop until
life was speeding down the evolutionary turnpike.

 While searching for that ancient precursor of life last April, Scripps
Research Institute's Joyce stumbled on the molecule that so tantalized him.
A bit of synthetic RNA sloshing around in a test tube suddenly attached
itself to a piece of protein and embarked on a course of nonstop
replication. For a moment, this molecular upstart seemed close to the
breakthrough Joyce had been seeking.

 The molecule, he acknowledges, is not alive. Magical as it seems, it
cannot replicate without a steady supply of prefabricated proteins. To
qualify as living, a molecule would need to have the ability to reproduce
without outside help. An important step in this direction was recently
taken by Harvard molecular biologist Jack Szostak and his graduate student
David Bartel, who mimicked the prolific chemistry of primitive earth by
randomly generating trillions of different strands of RNA. Eventually the
scientists came up with a good five dozen that were able to join themselves
to other strands suspended in the same test tube. The process of linkage,
explains Szostak, is critical to the formation of complex molecules from
simple building blocks. What's exciting, he says, is this part of the
origin-of-life puzzle does not look quite so daunting as before.

 One of these days, both Joyce and Szostak believe, when someone fills a
test tube with just the right stuff, a self-replicating molecule will pop
up. If that happens, the achievement could be as upsetting as it is
amazing. For it would challenge the most fundamental conceptions of what
life is all about. Life, to most people, means animals or plants or
bacteria. Less clear cut are viruses, because they are nothing more than
strands of nucleic acid encased in protein, and they cannot reproduce
outside a living cell.

 As scientists close in on life's origins, the working definition of life
will be pondered, debated and perhaps even expanded. If a sliver of fully
functional RNA arises in a test tube and starts building its own proteins,
who is to say it is any less alive than the strand of RNA doing the same
thing inside a cell?
 Some people will always hold to the belief that it is a divine spark, not
clever chemistry, that brings matter to life, and for all their fancy
equipment, scientists have yet to produce anything in a test tube that
would shake a Fundamentalist's faith. The molecule in Joyce's lab, after
all, is not as sophisticated as a virus and is still many orders of
magnitude less complex than a bacterium. Indeed, the more scientists learn
about it, the more extraordinary life seems. Just as the Big Bang theory
has not demystified the universe, so progress in understanding the origin
of life should ultimately enhance, not diminish, the wonder of it.

With reporting by David Bjerklie/New York, Barry Hillenbrand/London and
James O. Jackson/Gottingen


Copyright 1993 Time Inc. All rights reserved.