Biochemists uphold law of physics (EurkAlert)
Experiments by biochemists at the University of California, Davis show for the first time that a law of physics, the ergodic theorem, can be demonstrated by a collection of individual protein molecules — specifically, a protein that unwinds DNA. The work will be published online by the journal Nature on July 14.
The ergodic theorem, proposed by mathematician George Birkhoff in 1931, holds that if you follow an individual particle over an infinite amount of time, it will go through all the states that are seen in an infinite population at an instant in time. It’s a fundamental assumption in statistical mechanics — but difficult to prove in an experiment.
Using technology invented at UC Davis for watching single enzymes at work, Bian Liu, a graduate student in the Biophysics Graduate Group and professor Steve Kowalczykowski, Department of Microbiology and Molecular Genetics and UC Davis Cancer Center, found that when they paused and restarted a single molecule of the DNA-unwinding enzyme RecBCD, it could restart at any speed achieved by the whole population of enzymes.
Caption: RecBCD enzymes are unwinding DNA at different speeds. The bright ball at left is a bead, the bright strand is a stretch of DNA that shortens as it is unwound by the enzyme. The enzymes show ergodic behavior, supporting an important theory in statistical physics.
Credit: Bian Liu, UC Davis