Article Information

• PDF (721 kb)

PubMed

• Articles by R. Rikmenspoel
• Articles by A.C. Jacklet

Related Articles

• Measurement of the Force Produced by an Intact Bull Sperm Fl...

  Measurement of the Force Produced by an Intact Bull Sperm Flagellum in Isometric Arrest and Estimation of the Dynein Stall Force Biophysical Journal, Volume 79, Issue 1, 1 July 2000, Pages 468-478 Kathleen A. Schmitz, Dana L. Holcomb-Wygle, Danial J. Oberski and Charles B. Lindemann Abstract The force generated by a detergent-extracted reactivated bull sperm flagellum during an isometric stall was measured with a force-calibrated glass microprobe. The average isometric stall force from 48 individual measurements was 2.5±0.7×10dyne (2.5±0.7×10N). The force measurements were obtained by positioning a calibrated microprobe in the beat path of sperm cells that were stuck by their heads to a glass microscope slide. The average position of the contact point of the flagellum with the probe was 15m from the head-tail junction. This average lever arm length multiplied by the measured force yields an estimate of the active bending moment (torque) of 3.9×10 dyne×cm (3.9×10N×m). The force was sustained and was for the most part uniform, despite the fact that the flagellum beyond the point of contact with the probe usually continued beating. It appears that the dynein motors in the basal portion of the flagellum continue to pull in an isometric stall for as long as the motion of the flagellum is blocked. If dynein motors in the flagellum distal to the contact point with the probe were contributing force to the displacement of the probe, then the flagellar segment immediately past the point of contact would have to show a net curvature in the direction of the probe displacement. No such curvature bias was observed in the R-bend arrests, and only a small positive curvature bias was measured in the P-bend arrests. Our analysis of the data suggests that more than 90% of the sustained force component is generated by the part of the flagellum between the probe and the flagellar base. Based on this premise, the isometric stall force per dynein head is estimated to be 5.0×10 dyne (5pN). This equals ∼1.0×10 dyne (10 pN) per intact dynein arm. These values are close to the isometric stall force of isolated dynein. This suggests that all of the dynein heads between the base and the probe, on the active side of the axoneme, are contributing to the force exerted against the probe. Abstract | Full Text | PDF (314 kb)

• Organelle Size Regulation: Length Matters

  Organelle Size Regulation: Length Matters Current Biology, Volume 13, Issue 13, 1 July 2003, Pages R506-R507 Joel Rosenbaum Summary The control of flagellar length can be easily studied in the model genetic cell . Recent work has revealed that the mutant gene in a long-flagella mutant encodes a protein kinase. Summary | Full Text | PDF (674 kb)

• Coarse-Grained Molecular Dynamics Simulations of a Rotating ...

  Coarse-Grained Molecular Dynamics Simulations of a Rotating Bacterial Flagellum Biophysical Journal, Volume 91, Issue 12, 15 December 2006, Pages 4589-4597 Anton Arkhipov, Peter L. Freddolino, Katsumi Imada, Keiichi Namba and Klaus Schulten Abstract Many types of bacteria propel themselves using elongated structures known as flagella. The bacterial flagellar filament is a relatively simple and well-studied macromolecular assembly, which assumes different helical shapes when rotated in different directions. This polymorphism enables a bacterium to switch between running and tumbling modes; however, the mechanism governing the filament polymorphism is not completely understood. Here we report a study of the bacterial flagellar filament using numerical simulations that employ a novel coarse-grained molecular dynamics method. The simulations reveal the dynamics of a half-micrometer-long flagellum segment on a timescale of tens of microseconds. Depending on the rotation direction, specific modes of filament coiling and arrangement of monomers are observed, in qualitative agreement with experimental observations of flagellar polymorphism. We find that solvent-protein interactions are likely to contribute to the polymorphic helical shapes of the filament. Abstract | Full Text | PDF (931 kb)

• …more

Abstract

The flagellar length of cricket spermatozoa was reduced in steps from congruent to 1,000 micrometer (intact length) to 50 micrometer. In intact sperm the flagellar wave properties were largely independent of the viscosity of the external medium. When the flagellar length had been reduced to less than 100 micrometer the flagellar frequency was reduced at a raised external viscosity. Independent motion of different sections of a flagellum was not observed when its length is less than 100 micrometer. It is concluded that in long thin flagella, transverse viscous forces cannot exert a moment beyond a lever length of approximately 100 micrometer. It is shown that the existence of a maximum lever length, beyond which no moment can be transmitted, leads to the absence of a standing active contractile moment in the long insect sperm.