Self and the Beginning of Life 47“9x6” b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanitythat nature did not provide such special containers when life was starting
to germinate. Without a confinement, all the reactants would have been
infinitely diluted and the chemistry of life could not have taken place,
since the rate of a chemical reaction is concentration dependent (the law
of mass action). A number of possibilities have been suggested, ranging
from Darwin’s “warm little pond” to lagoons, to volcanic hot springs,
and to deep-sea hydrothermal vents, but none is considered satisfactory.
Making a cell membrane requires lipids, which normally are made by
enzymes. A ray of hope comes from the possibility that certain types of
clay could catalyze the formation of fatty acids, and that clay could also
convert fatty acids into cell-like vesicles.
Szostak and his coworkers showed that, in the test tube, simple
fatty acids can form cell-like spheres that permit small molecules (such
as amino acids and nucleotides) to get in, but prevent long RNA chains
to diffuse out. Adding more fatty acid molecules to the mix permits the
spheres to grow in size. Subsequent shearing of the larger spheres causes
them to break apart into smaller ones, in a sense simulating cell division.^45
3.14 The Power of Mineral Catalysis
Many metals are known catalysts for inorganic and organic reactions.
In modern biochemistry, metal ions are essential components (serving as
cofactors) in many enzyme systems. Examples include magnesium, man-
ganese, copper, iron, nickel, zinc, cobalt and molybdenum. These and
other metals are found in nature in the form of clays and were likely to
be available in the early Earth. It is reasonable to assume that, before the
advent of macromolecular catalysts (protein enzymes and ribozymes),
metal ions could have ignited the first spark of life. Minerals in clays
could serve as centers for carbon fixation and for anchoring growing car-
bon chains, promoting localized reactions in an otherwise chaotic chem-
ical mix. Such immobilization would solve the dilution problem for the
biopolymers, though it would not control other environmental factors
such as pH, ionic strength, and the availability of small molecules.