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ISTthe chemical reactions that allow plant
and animal cells to produce energy. And
those chemical reactions depend on the
basic fact that the membrane is an oily
structure interacting with a watery cell
inside of it.
But the team won’t be using methane
or ethane, the liquid hydrocarbons that
fill Titan’s lakes, for its experiments.
Those substances are liquids only when
exposed to incredibly cold temperatures
like those found on Titan’s surface, not
those usually found in chemistry labs
on Earth. Instead, the researchers are
sticking with hydrocarbons like hexane,
which is a good analogue for methane
but stays in liquid form at room tem-
perature, as well as chloroform and
others. The boundaries of these droplets
— where oil meets water — serve as a
simple analogue for the early develop-
ment of cell membranes.
Maurer’s experiments won’t produce
anything you could reasonably call a
cell membrane, but they just might shed
some light on the basic chemistry that can
occur at the boundary of oil and water.
“We kind of need this
oil phase in our cells to
drive energy generation,”
says Maurer, “and so it makes
sense that you could, in some way,
make an oil droplet have functionality
that’s similar to an aqueous cell by using
the surface of the oil droplet to drive
reactions.”
This team isn’t the first to think about
the idea of alien cell membranes. In a
2015 Science Advances paper, planetary
scientist Jonathan Lunine of Cornell
University, working with two chemical
engineers (none of the three is involved
in Bracher’s project), used digital model-
ing to determine that vinyl cyanide — a
compound made of nitrogen, carbon,
and hydrogen, also called acrylonitrile
— could theoretically form rudimentary
barriers in methane.
“To call it a membrane would be to give
it too much credit, but it’s at least some-
thing [that] kind of encloses and could
create a kind of container,” Lunine says. In
2016, he and chemist Martin Rahm (then
at Cornell, and currently at Chalmers
University of Technology) digitally mod-
eled compounds of hydrogen cyanide,
showing they could bind together
to form sheets and rolls in a
simulated hydrocarbon sea.
And then in 2017, another
paper published in Science
Advances announced the
discovery of evidence for
vinyl cyanide on Titan,
marking a step forward
in the search for molecules
capable of supporting life on the
distant moon.
Back on Earth, Maurer’s experiment
is simple. She and her colleagues want to
see if they can get compounds to cross
that oil-water boundary at all. They’ll start
with the familiar genetic molecules DNA
and RNA, but these will need some help
crossing over. The backbone of nucleic
acids like DNA and RNA is a chain of
smaller molecules called phosphates,
which have a slight negative charge. But
WATER AND LIFE
Water is a polar molecule consisting of two hydrogen atoms and one oxygen atom.
The oxygen atom in one water molecule tends to be attracted to a hydrogen atom in a
neighboring water molecule, and vice versa, giving water its unique properties. These
properties are essential for the chemistry of life on Earth.
For the chemical processes of life to happen, molecules must be able to connect,
separate, and reconnect in specific ways. Think about DNA replication, for instance.
The base pairs that make up the genetic code bond when their negatively charged
hydrogen atoms are attracted to positively charged atoms in another nucleotide. Those
bonds hold the two strands of the double helix together, but because the hydrogen
in water molecules also bonds this way, it’s relatively easy for enzymes to “unzip” the
double helix for replication, then bind the two new strands together again.
However, the molecules of life won’t work in hydrocarbons the way they do in water.
That’s because most hydrocarbons don’t tend to form hydrogen bonds. But it’s possible
that other molecules floating around in a lake of methane could bond and react in ways
that let them carry out the basic chemical functions of life. — K.N.S.
Hydrothermal vents form when seawater enters
fissures in the ocean floor, is heated by the hot
magma beneath, and boils back up through the
cracks. The vents are often teeming with life,
including microorganisms that convert minerals
and other chemicals into energy. Such vents
could provide a hospitable environment for life
elsewhere in the universe as well.OUT THERE