Inside the cell, an ocean of buffeting waves

 A new biophysical study led by researchers at Harvard University reveals that the cytoplasm is actually an elastic gel, so it puts up some resistance to simple diffusion. But energetic processes elsewhere in the cell—in the cytoskeleton, especially—create random but powerful waves in the cytoplasm, pushing on proteins and organelles alike. Like flotsam and jetsam buffeted by the wakes of passing ships, suspended particles scatter much more quickly and widely than they would in a calm sea.

Because transport within the cytoplasm therefore depends mainly on separate processes that consume energy, a measurement of the spectrum of forces exerted on the cytoplasm at any given time can provide a snapshot of the metabolic state of the cell.

Led by David A. Weitz, Mallinckrodt Professor of Physics and Applied Physics at the Harvard School of Engineering and Applied Sciences (SEAS), a team of applied physicists and cell biologists have put forth this new model of the cytoplasm and demonstrated a way to quantify the aggregate forces felt by particles and organelles in the cell. Their findings, published online August 14 in the journal Cell, raise a host of new questions about cellular dynamics. They also provide a robust new tool for future investigations.

"Our research provides the first real physical understanding of the cytoplasm in mammalian cells," says lead author Ming Guo, Ph.D. ‘14, a former graduate student in applied physics at Harvard SEAS who is now continuing as a postdoctoral fellow to further explore the fundamental biophysics of cells. "This work is going to be critical for future research on development, cancer biology, and metabolism."

Caption: Within the cytoplasm, fluctuating forces enhance the intracellular transport of proteins and organelles. Credit: Image courtesy of Ming Guo, Harvard SEAS.

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