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Life on Mars?
Detecting amino acids on the red planet

by Robert Sanders

Chemistry professor Richard Mathies and his colleagues are working on an instrument that would use gene sequencing technologies to probe Mars dust for evidence of life-based amino acids, the building blocks of proteins. With two development grants from NASA totaling nearly $2.4 million, he and his collaborators hope to build a Mars Organic Analyzer (MOA) to fly aboard NASA's roving, robotic Mars Science Laboratory mission and/or the European Space Agency's ExoMars mission, both scheduled for launch in 2009.

The MOA looks not only for the chemical signature of amino acids, but tests for a critical characteristic of life-based amino acids: They’re all left-handed. Amino acids can be made by physical processes in space—they’re often found in meteorites—but they’re about equally left- and right-handed. If amino acids on Mars have a preference for left- handed over right-handed amino acids, or vice versa, they could only have come from some life form on the planet, Mathies said.

“We feel that measuring homochirality—a prevalence of one type of handedness over another—would be absolute proof of life,” said Mathies, a member of the California Institute for Quantitative Biomedical Research (QB3) . “That’s why we focused on this type of experiment. If we go to Mars and find amino acids but don’t measure their chirality, we’re going to feel very foolish. Our instrument can do it.”

Amino acids, the building blocks of proteins, can exist in two mirror-image forms, designated L (levo) for left-handed and D (dextro) for right-handed. All proteins on Earth are composed of amino acids of the L type, allowing a chain of them to fold up nicely into a compact protein. “After amino acids are detected, the labeled amino acid solution is pumped down into microfluidics and crudely separated by charge,” Mathies said. “The mobility of the amino acids tells us something about charge and size and, when cyclodextrins are present, whether we have a racemic mixture, that is, an equal amount of left- and right-handed amino acids. If we do, the amino acids could be non-biological. But if we see a chiral excess, we know the amino acids have to be biological in origin.”

The state-of-the-art chip, designed and built by graduate student Allison Skelley, consists of channels etched by photolithographic techniques and a microfluidic pumping system sandwiched into a four-layer disk four inches in diameter.

Related sites:

astrobiology.berkeley.edu

Richard Mathies website




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