A. E. Pelling, S.Sehati, E. B. Gralla, J. S. Valentine, and J. K. Gimzewski, “Local Nanomechanical Motion of the Cell Wall of Saccharomyces cerevisiae," Science, 305, 1147-1150 (2004)
Like passing freight trains that shake the walls of nearby houses, cargo-carrying proteins shake the cell walls of yeast. Gimzewski's team measured these tiny cell wall vibrations in a species of yeast used to make bread rise. They performed many experiments to try to understand what makes the cell walls vibrate. They think that the protein freight carriers, also called molecular motors, cause the wall vibrations as they transport everything from bits of protein to whole chromosomes throughout the cell.
Since sound is created by vibrations, the scientists also determined how the cell wall movements would sound if they could be heard. If the yeast cell was the size of a human, the sounds it would make would not be like loud music. "They would be more like the sounds of an ordinary conversation," said Gimzewski. Gimzewski thinks sound is an interesting way to present observations of vibrating cell walls. The movements are too small and fast to be seen on video.
To investigate why the cells vibrate, Gimzewski studied the vibrations at different temperatures. They also treated yeast cells with a chemical that prevents the cells from producing energy. The vibrations stopped when the cells stopped producing energy. From these and a few other experiments and calculations, the scientists say that cell wall motion in yeast is probably caused by the activity of many molecular motors working within the cell at the same time. Gimzewski thinks these movements might be useful to the yeast cells. The motion could be part of a communication pathway or a pumping action that helps move nutrients or chemicals from one side of the cell wall to the other.