Courtesy American Institute of Physics
and World Science staff
Biology is chock full of art. For decades, scientists have probed some of the tiniest structures of life’s bas ic build ing molecular blocks, such as DNA or pro teins, rendering full-color ball-and-stick models of them that fill the pages of journals and adorn the trophy cases of biology depart ments every where.
While these representations reveal some of the most intricate molecular details of life, they of ten fall short in depicting how a molecule moves.
Just as the perfect picture of a horse can not convey the fluidity of it gallop, so does a frozen pic ture of DNA fail in describing its intricate dance.
“These are wet, warm, squishy things,” said Adam Cohen of Harvard University. They jiggle, they flap, they twist, they turn, and they randomly “walk” about.
Studying how a single molecule moves is hard, how ever, because of these very motions. Like a horse, if you set a single molecule free, it will wander away. You can tie it down, ensuring that it no longer wanders, but then you can’t necessarily observe how it moves.
Now, thanks to a machine built by Cohen and colleagues at Harvard, it may be possible to con fine a single molecule and study its motions at the same time. Cohen presented his findings this week in Boston at the annual symposium and exhibition of the American Vacuum Society, a part of the American Institute of Physics.
The machine basically uses a variable electric field to trap a single molecule under a microscope, Cohen said. It does this by tracking the molecule’s motion and then rapidly applying tiny electric pulses to counter this motion and zap the molcule back in to place. Cohen described how he and his colleagues can use this machine to look at things like virus particles or single pieces of DNA.
Cohen reported that his group recently made a movie by capturing 60,000 high-speed frames of a DNA molecule dancing. The studies show the nature of the molecule’s internal forces, said Co hen, and these properties give in formation about how DNA interacts in a biological setting.
“These are wet, warm, squishy things,” said Ad am Co hen of Har vard Uni ver s ity. They jig gle, they flap, they twist, they turn, and they ran domly “walk” about.
Stud y ing how a sin gle mol e cule moves is hard, how ev er, because of these very mo tions. Like a horse, if you set a sin gle mol e cule free, it will wan der away. You can tie it down, ensur ing that it no long er wan ders, but then you can’t nec essarily ob serve how it moves.
Now, thanks to a ma chine built by Co hen and col leagues at Har vard, it may be pos si ble to con fine a sin gle mol e cule and study its mo tions at the same time. Co hen pre sented his findings this week in Bos ton at the an nu al sym po si um and ex hibi tion of the Amer i can Vac u um So ci e ty, a part of the Amer can In sti tute of Phys ics.
The ma chine bas ic ally uses a var i a ble elec tric field to trap a sin gle mol e cule un der a mi cro scope, Co hen said. It does this by track ing the mol e cule’s mo tion and then rap idly ap ply ing ti ny elec tric pulses to count er this mo tion and zap the mol cule back in to place. Co hen de scribed how he and his colleagues can use this ma chine to look at things like vi rus par i cles or sin gle pieces of DNA.
Co hen re ported that his group re cently made a mov ie by cap tur ing 60,000 high-speed frames of a DNA mol e cule dancing. The stud ies show the na ture of the mol e cule’s in ter nal forc es, said Co hen, and the
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