The covalent oscillator: A paradigm accounting for the sliding/bending mechanism and wave propagation in cilia and flagella

1. The trophozoites of Selenidium fallax propagate bending waves at rates of up to 35 microns s-1, of a similar character to those manifested by eukaryotic cilia and flagella. A beat frequency of 0.12-0.15 Hz appears average, though rates outside this range have been recorded. Translatory locomotion at up to 6 microns s-1 has been observed. The protozoan demonstrates the presence of an active bending mechanism, probably along its entire length, and a means of coordinating adjacent bends. 2. The Reynolds number for the motion in 10(−5)-10(−4), suggesting that the hydrodynamic aspects of the trophozoite movement are amenable to analysis by similar means to those already employed for cilia and flagella. 3. It is possible that the protozoans exhibit a sliding microtubule mechanism, which could be very usefully compared with that occurring in the ciliary axoneme.

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Electron Microscopy of Shock Loaded Polycrystalline Beryllium

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100052547 ◽

1974 ◽

Vol 32 ◽

pp. 506-507 ◽

Cited By ~ 1

Author(s):

J. M. Galbraith ◽

L. E. Murr ◽

A. L. Stevens

Keyword(s):

Electron Microscopy ◽

Wave Propagation ◽

Structural Change ◽

Single Crystal ◽

Diffraction Pattern ◽

Shock Loading ◽

Slip Systems ◽

Compression Tests ◽

X Ray Diffraction ◽

X Ray

Uniaxial compression tests and hydrostatic tests at pressures up to 27 kbars have been performed to determine operating slip systems in single crystal and polycrystal1ine beryllium. A recent study has been made of wave propagation in single crystal beryllium by shock loading to selectively activate various slip systems, and this has been followed by a study of wave propagation and spallation in textured, polycrystal1ine beryllium. An alteration in the X-ray diffraction pattern has been noted after shock loading, but this alteration has not yet been correlated with any structural change occurring during shock loading of polycrystal1ine beryllium.This study is being conducted in an effort to characterize the effects of shock loading on textured, polycrystal1ine beryllium. Samples were fabricated from a billet of Kawecki-Berylco hot pressed HP-10 beryllium.

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Study of eukaryotic flagellar components by cryo-electron microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100142141 ◽

1986 ◽

Vol 44 ◽

pp. 98-101

Author(s):

John M. Murray ◽

Rob Ward

Keyword(s):

Electron Microscopy ◽

Primary Motion ◽

Cryo Electron Microscopy ◽

Cross Links ◽

Cilia And Flagella

The eukaryotic flagellum is constructed from 11 parallel tubular elements arranged as 9 peripheral fibers (doublet microtubules) and 2 central fibers (singlet microtubules). The primary motion generating component has been found to be arranged as axially periodic “arms” bridging the adjacent doublets. The dynein, comprising the arms, has been isolated and characterized from several different cilia and flagella. Various radial and azimuthal cross-links stabilize the axially aligned microtubules, and probably play some role in controlling the form of the flagella beat cycle.

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Observations of Frozen-Hydrated Microtubules

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100181270 ◽

1990 ◽

Vol 48 (1) ◽

pp. 504-505

Author(s):

D. Chrétien ◽

D. Job ◽

R.H. Wade

Keyword(s):

Fourier Transforms ◽

Structural Complexity ◽

Image Contrast ◽

Phase Behaviour ◽

Experimental Conditions ◽

Thin Sections ◽

Surface Lattice ◽

Cilia And Flagella ◽

Outstanding Question

Microtubules are filamentary structures found in the cytoplasm of eukaryotic cells, where, together with actin and intermediate filaments, they form the components of the cytoskeleton. They have many functions and show various levels of structural complexity as witnessed by the singlet, doublet and triplet structures involved in the architecture of centrioles, basal bodies, cilia and flagella. The accepted microtubule model consists of a 25 nm diameter hollow tube with a wall made up of 13 paraxial protofilaments (pf). Each pf is a string of aligned tubulin dimers. Some results have suggested that the pfs follow a superhelix. To understand how microtubules function in the cell an accurate model of the surface lattice is one of the requirements. For example the 9x2 architecture of the axoneme will depend on the organisation of its component microtubules. We should also note that microtubules with different numbers of pfs have been observed in thin sections of cellular and of in-vitro material. An outstanding question is how does the surface lattice adjust to these different pf numbers?We have been using cryo-electron microscopy of frozen-hydrated samples to study in-vitro assembled microtubules. The experimental conditions are described in detail in this reference. The results obtained in conjunction with thin sections of similar specimens and with axoneme outer doublet fragments have already allowed us to characterise the image contrast of 13, 14 and 15 pf microtubules on the basis of the measured image widths, of the the image contrast symmetry and of the amplitude and phase behaviour along the equator in the computed Fourier transforms. The contrast variations along individual microtubule images can be interpreted in terms of the geometry of the microtubule surface lattice. We can extend these results and make some reasonable predictions about the probable surface lattices in the case of other pf numbers, see Table 1. Figure 1 shows observed images with which these predictions can be compared.

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Introductory Remarks

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s1431927600002646 ◽

1980 ◽

Vol 38 ◽

pp. 598-599

Author(s):

H. Mohri

Keyword(s):

Muscle Contraction ◽

Experimental Evidence ◽

Sea Urchin ◽

Constant Length ◽

Thin Filaments ◽

Bridge Formation ◽

Thick Filaments ◽

Sliding Mechanism ◽

Radial Spokes ◽

Cilia And Flagella

In 1959, Afzelius observed the presence of two rows of arms projecting from each outer doublet microtubule of the so-called 9 + 2 pattern of cilia and flagella, and suggested a possibility that the outer doublet microtubules slide with respect to each other with the aid of these arms during ciliary and flagellar movement. The identification of the arms as an ATPase, dynein, by Gibbons (1963)strengthened this hypothesis, since the ATPase-bearing heads of myosin molecules projecting from the thick filaments pull the thin filaments by cross-bridge formation during muscle contraction. The first experimental evidence for the sliding mechanism in cilia and flagella was obtained by examining the tip patterns of molluscan gill cilia by Satir (1965) who observed constant length of the microtubules during ciliary bending. Further evidence for the sliding-tubule mechanism was given by Summers and Gibbons (1971), using trypsin-treated axonemal fragments of sea urchin spermatozoa. Upon the addition of ATP, the outer doublets telescoped out from these fragments and the total length reached up to seven or more times that of the original fragment. Thus, the arms on a certain doublet microtubule can walk along the adjacent doublet when the doublet microtubules are disconnected by digestion of the interdoublet links which connect them with each other, or the radial spokes which connect them with the central pair-central sheath complex as illustrated in Fig. 1. On the basis of these pioneer works, the sliding-tubule mechanism has been established as one of the basic mechanisms for ciliary and flagellar movement.

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