John F. McGowan
GFT Group Incorporated
It is suggested that life originated in a three-step process referred to as the jigsaw model. RNA, proteins, or similar organic molecules polymerized in a dehydrated carbon-rich environment, on surfaces in a carbon-rich environment, or in another environment where polymerization occurs. These polymers subsequently entered an aqueous environment where they folded into compact structures. It is argued that the folding of randomly generated polymers in water tends to partition the folded polymer into domains with hydrophobic cores and matching shapes to minimize energy. In the aqueous environment, hydrolysis or other reactions fragmented the compact structures into two or more matching molecules, occasionally producing simple living systems. It is argued that the hydrolysis of folded polymers such as RNA or proteins is not random. The hydrophobic cores of the domains are rarely bisected due to the energy requirements in water. Hydrolysis preferentially fragments the folded polymers into pieces with complementary structures and chemical affinities. Thus the probability of synthesizing a system of matched, interacting molecules in prebiotic chemistry is much higher than usually estimated. Environments where this process may occur are identified. The implications of this hypothesis for seeking life or prebiotic chemistry in the Solar System and the laboratory are explored.
Step 1: A primordial soup with amino
acids or similar monomers, possibly a
deposit of primordial hydrocarbons
similar to the chemicals in carbonaceous
chondrites, a kind of meteorite.
Step 2: The monomers polymerize into a
protein alpha-helix or similar helical
structure on the surface of a chiral crystal
that selects for the handedness of the
amino acids or other monomers.
Step 3: The helix is unstable because it has exposed hydrophobic residues (red spheres). It folds into a disk-shaped structure made of stable folding domains that have hydrophobic cores and matching shapes that fit together like a lock-and-key.
Step 4: Hydrolysis fragments the folded
polymer into four domains with
hydrophobic cores (red spheres) and
matching surfaces (green spheres for non-
hydrophobic residues). Each domain is a
wedge-shaped four-helix bundle.
Step 5: The domains catalyze the
polymerization of the matching faces of
the adjacent domains. Each face consists
of two alpha helices with exposed
hydrophobic residues. After
polymerization, each domain becomes a
half of the original structure.
Step 6: The halves recombine, burying
the hydrophobic residues, releasing
energy to perpetuate the process.
Step 7: For illustrative purposes the ends
of the structures have been ignored. This
is solved, for example, if the original alpha
helix folds into a donut-shaped structure
(torus) comprised of the disk-shaped
structures. The axial faces of the disk-
shaped structures fit together like a lock-
Reference: John F. McGowan, III, "Jigsaw model of the origin of life", in Instruments, Methods, and Missions for Astrobiology IV, Richard B. Hoover, Gilbert V. Levin, Roland R. Paepe, Alexei Yu. Rozanov, Editors, Proceedings of the SPIE Vol. 4495, pp. 199-210 (2002) (http://www.jmcgowan.com/JigsawPreprint.pdf)