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BP: Fachverband Biologische Physik
BP 26: Biophysics II: Mechanics and Flow in Biological Systems (joint AG jDPG, BP)
BP 26.2: Hauptvortrag
Donnerstag, 17. März 2011, 11:00–11:30, HSZ 201
What sperm head wiggling can tell us about flagellar hydrodynamics — •B.M. Friedrich1, I.H. Riedel-Kruse3, J. Howard4, and F. Julicher2 — 1Weizmann Institute of Science - Department of Materials and Interfaces, Rehovot, Israel — 2Max-Planck-Institute for the Physics of Complex Systems, Dresden, Germany — 3Stanford University, Stanford, USA — 4Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
Sperm cells propel themselves in a liquid by generating regular bending waves of their whip-like flagellum. At the relevant length and time scales of sperm swimming, inertia is negligible and self-propulsion is achieved purely by viscous forces. The shape of the flagellar beat determines the path along which a sperm cells swims.
To test a simple hydrodynamic theory of flagellar propulsion known as resistive force theory, we conducted high-precision measurements of the head and flagellum motions during circular swimming of bull spermatozoa near a surface. On short time-scales, the sperm head "wiggled" around an averaged path with the frequency of the flagellar beat. We found that the fine-structure of sperm swimming represented by this rapid wiggling is, to high accuracy, accounted for by resistive force theory and results from balancing forces and torques generated by the beating flagellum. By comparing experiment and theory, we could determine the hydrodynamic friction coefficients of the flagellum.
On time-scales longer than the flagellar beat cycle, sperm cells followed circular paths of non-zero curvature due to an asymmetry of their flagellar bending waves, in agreement with quantitative predictions of resistive force theory.
Finally, I will discuss how sperm cells can actively regulate the non-zero curvature of their swimming paths and address the relation to sperm navigation in a concentration gradient of a chemoattractant.
References J. Gray, G. T. Hancock, J. exp. Biol. 32 (1955). B.M. Friedrich, I.H. Riedel-Kruse, J. Howard, F. Julicher, J. exp. Biol. 213 (2010).