Media highlights in the January issues of Biophysic...( Bethesda MD The January 1st and Jan...)

Bethesda, MD The January 1st and January 15th issues of Biophysical Journal, published by the Biophysical Society, is now available online. Topics of interest include ciliates, force, spasmoneme, H2A/H2B, nucleosome, AFM, aquaporin, elasticity, and epithelial cells.

Volume 94, Issue 1, January 1, 2008

Power-limited contraction dynamics of Vorticella convallaria: an ultra-fast biological spring
Arpita Upadhyaya, Massachusetts Institute of Technology Mara Baraban, Massachusetts Institute of Technology Jacqueline Wong, Massachusetts Institute of Technology Paul T. Matsudaira, Whitehead Institute, MIT Alexander van Oudenaarden, Massachusetts Institute of Technology L.. Mahadevan, Harvard University
Keywords: ciliates; force; spasmoneme; velocity; viscosity

Speed is not characteristic of the microscopic movements common in biology where even fast cells typically move only about a body length every second. However, speed is what singles out the ultra-fast motion of a single-celled organism, Vorticella, as the stalk by which it is attached to a substrate contracts by coiling into a helix. The cell body is but a few microns in size, and yet can move at velocities of a few cm/s, i.e. it travels thousands of body lengths in a second. Our work quantifies the dynamics of this unusual spring-like engine and shows that this rapid movement is ultimately limited by the maximum power available when the stalk contracts, just as in a simple mechanical spring that is compressed and then suddenly released. However, unlike in a mechanical spring which stores and releases mechanical energy passively, in the contracting stalk of Vorticella, there is a dynamical conversion of one form of energy (electrostatic) into another (conformational) which process sets the ultimate internal physical limits on the performance of this mechano-chemical engine.