to Origins of Life Research
[J. Lucentini, "Darkness before Dawn", The Scientist 17:(23) 28-29, 2003]
Ultimate Goal is "creation of an artificial cell, as a model of a life system"
experimental approaches are active in today's research
...Search for sources of early precursor organic molecules of Life ???
search for bioorganic precursor molecules of life...
A) formed from a chemically reactive soup... in early oceans of Earth
1922 - Oparin & Haldane: suggest early Earth had a reducing atmosphere
early Earth rich in NH3, CH4, H2, & H2O
1953 - Miller & Urey ---> organics
> abiotic origin of organic molecules from simple inorganics
> H2O, NH3, CH4, & H2 in reducing atmosphere
> produce HCN and formaldehyde which leads to...
> amino acids, nucleotides, and sugars.
CRITICISM of research: was not really a reducing atmosphere, so chemically is unlikely
recently redone by J.L.
& S.L. Miller using a weakly reducing
atmosphere (irradiated with protons)... they obtained bioorganic compounds
in amounts comparable to those of Miller/Urey type experiments.
organic syntheses and origins of life timeline*
Deep dwelling (ocean)
(discovered in 1979)
with minerals spewing up from pressurized, hot springs...
vent areas are full of organically rich molecules ---> life (tube worms @ vents).
and bacteria living in hydrothermal vents
speculation is that life may have originated in vents regions.
Origins of Metabolism (a role of hydrothermal vents?)
Gunter Wachterschauser (german biochemist) has
speculated that origins of
bioorganic chemical reactivity may have originated at hydrothermal vents.
> earliest primordial biochemical cycles may have functioned there
> metabolic cycles likely predate cells...
took place on mineral surfaces
that acted as catalysts & surfaces for early reactions
> key reaction may have been a reductive reaction like citric acid cycle
CO + oxidation of vent minerals --> reduction
Groups including M.J. Russell,
C. Huber, and G. Cody
have synthesized amino acids and assembled/disassembled polypeptides
all crucial metabolic processes that might have arisen via hydrothermal vents.
Origins Cellular Life by Deamer essay
but maybe, there was a possible Role for Minerals* in Earth's chemical evolution
Source of Bioorganic molecules
(the precursors to life?)
a) Miller & Urey - abiotic synthesis
b) hydrothermal vents (spewed up from "middle Earth")
C) SPACE DEBRIS: (as seen thru today's living microbes)
chemical evolution vs. meteorite
dust, meteorites, asteroids, & comets may have deposited
organics on newly formed planet Earth.
Comets are mostly ice crystals on cores of silicates & carbon
contain about 10% CO, CO2, CH4, CH3OH, and NH3
Asteroids rocky objects, that hit Earth & contain molecules such as...
kerogen [a PAH], nucleobases, quinones, carboxylic acids,
amines & amides = some 70 amino acids, including 8 of common 20 aa's.
? while Miller & Urey's soup had 50%/50% mix of D & L aa's optical isomers,
asteroid aa's have a surplus of L-aa's, as in today's proteins (argues for asteroids).
(NASA - 1999)
reactions in the lab,
to look at molecular events within comets... he has observed...
> chemical reactions can occur even in very low temps [25K (-400oF)],
> UV light can break chemical bonds
- forming ketones, esters, alcohols, and quinones (for e- transport).
> some molecules formed spherical, capsule-like droplets when
exposed to water, with properties akin to cell membranes.
some other Astrobiology & Extraterrestrial
PANSPERMIA - idea that living microbes drifted in from space & colonized Earth;
Svante Arrhenius (1908) radiation emitted by stars carried
microbes thru space; (also supported by Francis Crick)
SETI - Universe some 1020 stars with properties similar to our sun's [?]
if 10% have planetary systems &
if 1/10,000 has a planet equal in size & properties to earth
then life as we known it (carbon based life forms) may still
occur on as many as 1015 planets (Carl Sagan & Fred Hoyle)
a speculation ??? extraterrestrial aa's built 1st proteins ?
(optional: Some historical perspective: Ideas on the origins of Life.)
2nd experimental approaches of origins of life research
II) Evolution of an RNA world... (which came 1st DNA or RNA)
in 1989 Sidney Altman and Thomas Cech - received
for demonstrating that RNA molecules (RIBOZYMES) have CATALYTIC ACTIVITY
i.e., these RNA's catalyze hydrolysis & condensation rxs of phosphodiester bonds.
RNA can be a template and also
catalyze polymerization of like molecules,
i.e., replicate itself, then RNA molecules may have been the 1st
SELF-REPLICATING living entity.
RNA molecules exists naturally today, but lab experimentation may
establish that it was feasible, and that RNA molecules can be selected for via
Darwinian evolutionary mechanisms (natural selection).
3rd experimental approaches of origins of life research
III) Knock-out Cells...
By modifying a simple microbe, scientists hope to create a new form of single cell life.
J. Craig Venter, a principle investigator (P.I.) of
the Human Genome Project is attempting
to make a new type of bacterium using DNA manufactured in the lab.
> using the sequenced the genes of a bacterium called Mycoplasma genitalium, a gram-positive
parasitic bacterium, whose primary infection site may be the human urogenital tract.
It probably causes non-gonococcal urethritis. It is one of the simplest microbes known
with only one chromosome and 517 genes.
> researchers began systematically removing genes to determine how many genes
were essential for life. In 1999, they published a paper that narrowed the needs
of M. genitalium to between 265 and 350 genes.
> a genomic goal will be to learn on a molecular level the minimum genes a cell needs to thrive
and reproduce and how to artificially make those and other genes.