Mice, Magnetism, and Reactions on Solids

Nobels awarded in genetics, materials science, and surface chemistry

The 2007 Nobel prizes in the sciences were announced early this week.

MAGNETIC SANDWICH. Modern hard disks read data as magnetic fields change the electrical resistance of a nanoscale circuit in the reading head. iStockphoto

Physiology or Medicine

The discovery of techniques to identify the roles of genes has earned three scientists the 2007 Nobel Prize in Physiology or Medicine.

The award is shared by Mario R. Capecchi of the Howard Hughes Medical Institute and the University of Utah in Salt Lake City, Martin J. Evans of Cardiff University in Wales, and Oliver Smithies of the University of North Carolina at Chapel Hill.

Nearly 3 decades ago, Capecchi and Smithies separately investigated the process that cells use to fix damaged genes. Both researchers managed to harness this process, called recombination. By injecting normal DNA into a cell, they were able to modify targeted genes.

But to test the actual roles of individual genes, the scientists needed to make the DNA changes in live organisms, not just in cells in a lab dish.

Across the Atlantic, Evans had discovered embryonic stem cells in mice. By adding cells from one mouse embryo to an embryo from a different kind of mouse, he was able to modify the genes passed along to the second animal’s offspring. Moreover, by using embryonic stem cells infected with a virus—and its DNA—Evans showed that it was possible to add genetic material to an embryo. The work suggested a way to alter an animal so that its eggs and sperm pass on those changes.

Scientists seized upon these breakthroughs as a means to determine what individual genes do by replacing genes with inactive versions in mice and then noting the consequences. In 1989, several laboratories published accounts of mice that were genetically engineered to lack particular genes and produced offspring with the same change.

The work had inaugurated a technique that would ultimately elucidate the roles of hundreds of genes.

“The best way to understand the function of a gene is to remove it,” says geneticist David W. Melton of the University of Edinburgh. “This technology, for the first time, generated an experimental system in mice that enabled us to study relationships between genetic changes and the symptoms of specific diseases.”

Few diseases are attributable to a single faulty gene. In recent years, Capecchi notes, scientists have gained the ability to assess several genes at once. “We want to see … how these genes interact with each other,” he says.

Capecchi was born in Italy in 1937. When his mother was imprisoned in Germany during World War II, he lived on the streets for 4 years before being reunited with her in 1945. They moved to the United States, where his studies put him on the ground floor of the burgeoning science of genetics.

Capecchi’s life has now come full circle in a story of rags to research to riches. He and the other two scientists will split the $1.54 million prize.—N. Seppa


In less than 10 years, a physical effect discovered in the lab made its way into computer technology, ultimately yielding dramatic improvements in data-storage capacity. The discoverers of that effect, Albert Fert of the Université Paris-Sud in Orsay, France, and Peter Grünberg of the Research Center Jülich in Germany, will share this year’s Nobel Prize in Physics.

The phenomenon, which each of the physicists’ teams observed independently in 1988, is called giant magnetoresistance. It has enabled engineers to increase the sensitivity of hard disk reading heads and pack more data into less space.

Certain metals, notably iron, are magnetic because their atoms, which act individually like small bar magnets, all tend to line up in the same direction. And when electrons flow through such a metal, constituting an electric current, their spins also tend to line up with the metal’s magnetization. That alignment allows the current to flow more easily.

Fert and Grünberg sought to exploit this fact in combination with another phenomenon. When two layers of a magnetic metal are brought next to each other, their magnetizations tend to turn so that their orientations match. But if a layer of a nonmagnetic metal, such as chromium, is sandwiched in between, the magnetizations of the two layers tend to line up in opposite directions.

The physicists reckoned that if they ran a current through such a layered structure, the electrons would align their spins parallel to the first layer’s magnetization, and then—if the nonmagnetic layer were just nanometers thin—would maintain that orientation as they crossed into the second magnetic layer. Because the electrons would have the wrong orientation for the third layer’s magnetization, they would encounter greater resistance.

Moreover, the researchers expected that if they applied an external field to force the magnetization of the two outer layers into the same orientation, the resistance would fall by a small percentage. Instead, it was cut in half.

“My first reaction was, ‘There must be some short circuit in our experiment,'” says Mario Baibich of the Universidade Federal do Rio Grande do Sul in Porto Alegre, Brazil, who was on Fert’s team in Orsay. But the phenomenon, dubbed giant magnetoresistance, was genuine.

The effect allows the sensitive detection of a magnetic field through the unexpectedly large change in resistance that it triggers.

IBM quickly took an interest in the new physics and first incorporated it into hard disks in 1997. Giant magnetoresistance has led to a 30-fold increase in hard disk–data densities since then.

Jordan Katine, a researcher at the Hitachi Global Storage Technologies Research Center in San Jose, Calif., says that older readout technologies would have soon reached their physical limits. “The industry was running out of steam in terms of how much information we could store in a given surface area.”—D. Castelvecchi


Not all chemistry takes place in test tubes. Atmospheric oxygen reacting with a copper gutter creates a green patina, for example. And under the right conditions, the surfaces of fine pieces of iron can turn nitrogen from the air into ammonia, useful in fertilizers.

Gerhard Ertl of the Fritz Haber Institute at the Max-Planck Society in Berlin, who studies such reactions, won this year’s Nobel Prize in Chemistry for laying the foundations of modern surface chemistry.

When a gas molecule hits a solid, it can bounce away, stick to the surface, or react with another gas molecule at the site. Studying these phenomena is a challenge because of the imperfections of any seemingly smooth surface.

“If you dive down and look at surfaces close up, atom by atom, they turn out to be landscapes, with ridges and mountains and valleys,” says chemist Andrea Sella of University College London.

Ertl figured out a way to get around these imperfections. He used single faces of crystals, each with perfectly arranged atoms, as stand-ins for larger surfaces. To keep a face clean enough to study, he performed experiments under high vacuum. These innovative methods are now common practice among surface chemists.

Insights derived from Ertl’s work apply not only to the weathering of copper and the manufacture of fertilizer but also to fuel cells creating electricity, catalytic converters turning an automobile’s carbon monoxide into carbon dioxide, and ozone-depleting chemicals reacting with ice crystals in the atmosphere.

“Ertl is certainly one of the people who has cast the most light on what happens on surfaces,” says Sella.—S. Williams

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