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    George Oster

    Two theoretical formalisms are widely used in modeling mechanochemical systems such as protein motors: continuum Fokker-Planck models and discrete kinetic models. Both have advantages and disadvantages. Here we present a “finite volume”... more
    Two theoretical formalisms are widely used in modeling mechanochemical systems such as protein motors: continuum Fokker-Planck models and discrete kinetic models. Both have advantages and disadvantages. Here we present a “finite volume” procedure to solve Fokker-Planck equations. The procedure relates the continuum equations to a discrete mechanochemical kinetic model while retaining many of the features of the continuum formulation. The resulting numerical algorithm is a generalization of the algorithm developed previously by Fricks, Wang, and Elston through relaxing the local linearization approximation of the potential functions, and a more accurate treatment of chemical transitions. The new algorithm dramatically reduces the number of numerical cells required for a prescribed accuracy. The kinetic models constructed in this fashion retain some features of the continuum potentials, so that the algorithm provides a systematic and consistent treatment of mechanical-chemical responses such as load-velocity relations, which are difficult to capture with a priori kinetic models. Several numerical examples are given to illustrate the performance of the method.
    Recent experiments have provided new quantitative measurements of the rippling phenomenon in fields of developing myxobacteria cells. These measurements have enabled us to develop a mathematical model for the ripple phenomenon on the... more
    Recent experiments have provided new quantitative measurements of the rippling phenomenon in fields of developing myxobacteria cells. These measurements have enabled us to develop a mathematical model for the ripple phenomenon on the basis of the biochemistry of the C-signaling system, whereby individuals signal by direct cell contact. The model quantitatively reproduces all of the experimental observations and illustrates how
    Many cell movements appear to be driven by the polymerization of actin. Here we show how the force of polymerization can be generated by the thermal motions of the actin filaments near the sites of polymerization. We apply the model to... more
    Many cell movements appear to be driven by the polymerization of actin. Here we show how the force of polymerization can be generated by the thermal motions of the actin filaments near the sites of polymerization. We apply the model to explain the observations that the lamellipodial cytoskeleton is organized into an orthogonal network interspersed with filopodial protrusions, and that
    ... THE VELIGER © CMS, Inc., 1986 A Model for Shell Patterns Based on Neural Activity by BARD ERMENTROUT ... 28, No.4 a b c Figure 1 Three fundamental classes of shell pigment markings on Bankivia fasciata: a, longitudinal bands; b,... more
    ... THE VELIGER © CMS, Inc., 1986 A Model for Shell Patterns Based on Neural Activity by BARD ERMENTROUT ... 28, No.4 a b c Figure 1 Three fundamental classes of shell pigment markings on Bankivia fasciata: a, longitudinal bands; b, incremental lines; c, oblique stripes. ...
    Three protein motors have been unambiguously identified as rotary engines: the bacterial flagellar motor and the two motors that constitute ATP synthase (F(0)F(1) ATPase). Of these, the bacterial flagellar motor and F(0) motors derive... more
    Three protein motors have been unambiguously identified as rotary engines: the bacterial flagellar motor and the two motors that constitute ATP synthase (F(0)F(1) ATPase). Of these, the bacterial flagellar motor and F(0) motors derive their energy from a transmembrane ion-motive force, whereas the F(1) motor is driven by ATP hydrolysis. Here, we review the current understanding of how these protein motors convert their energy supply into a rotary torque.
    Human keratinocytes migrate towards the negative pole in DC electric fields of physiological strength. This directional migration is promoted by epidermal growth factor (EGF). To investigate how EGF and its receptor (EGFR) regulate this... more
    Human keratinocytes migrate towards the negative pole in DC electric fields of physiological strength. This directional migration is promoted by epidermal growth factor (EGF). To investigate how EGF and its receptor (EGFR) regulate this directionality, we first examined the effect of protein tyrosine kinase inhibitors, including PD158780, a specific inhibitor for EGFR, on this response. At low concentrations, PD158780 inhibited
    We propose that protein translocation across membranes is driven by biased random thermal motion. This "Brownian ratchet" mechanism depends on chemical asymmetries between the cis and trans sides of the membrane. Several... more
    We propose that protein translocation across membranes is driven by biased random thermal motion. This "Brownian ratchet" mechanism depends on chemical asymmetries between the cis and trans sides of the membrane. Several mechanisms could contribute to rectifying the thermal motion of the protein, such as binding and dissociation of chaperonins to the translocating chain, chain coiling induced by pH and/or ionic gradients, glycosylation, and disulfide bond formation. This helps explain the robustness and promiscuity of these transport systems.
    The ornate and diverse patterns of seashells testify to the complexity of living systems. Provocative computational explorations have shown that similarly complex patterns may arise from the collective interaction of a small number of... more
    The ornate and diverse patterns of seashells testify to the complexity of living systems. Provocative computational explorations have shown that similarly complex patterns may arise from the collective interaction of a small number of rules. This suggests that, although a system may appear complex, it may still be understood in terms of simple principles. It is still debatable whether shell patterns emerge from some undiscovered simple principles, or are the consequence of an irreducibly complex interaction of many effects. Recent work by Boettiger, Ermentrout and Oster on the biological mechanisms of shell patterning has provided compelling evidence that, at least for this system, simplicity produces diversity and complexity.
    The elastic interaction of membrane inclusions provides one of the simplest physical realizations of multibody forces. Here we show how the cross-sectional shape of the inclusion greatly changes the character of the interaction, and... more
    The elastic interaction of membrane inclusions provides one of the simplest physical realizations of multibody forces. Here we show how the cross-sectional shape of the inclusion greatly changes the character of the interaction, and illustrates a pattern formation mechanism. The formalism provides a transparent framework for modeling bilayer-inclusion boundary effects on the multibody interaction.
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    ... complex systems. We shall not deal to any great extent with linear graph theory since it is adequately treated in the technical literature (Berge, 1962; Berge & Ghouila-Houri, 1965; Harary, 1969; Seshu & Reed,... more
    ... complex systems. We shall not deal to any great extent with linear graph theory since it is adequately treated in the technical literature (Berge, 1962; Berge & Ghouila-Houri, 1965; Harary, 1969; Seshu & Reed, 1961). The example ...
    Myxococcus xanthus is a Gram-negative, soil-dwelling bacterium that glides on surfaces, reversing direction approximately once every 6 min. Motility in M. xanthus is governed by the Che-like Frz pathway and the Ras-like Mgl pathway, which... more
    Myxococcus xanthus is a Gram-negative, soil-dwelling bacterium that glides on surfaces, reversing direction approximately once every 6 min. Motility in M. xanthus is governed by the Che-like Frz pathway and the Ras-like Mgl pathway, which together cause the cell to oscillate back and forth. Previously, Igoshin et al. (2004) suggested that the cellular oscillations are caused by cyclic changes in concentration of active Frz proteins that govern motility. In this study, we present a computational model that integrates both the Frz and Mgl pathways, and whose downstream components can be read as motor activity governing cellular reversals. This model faithfully reproduces wildtype and mutant behaviors by simulating individual protein knockouts. In addition, the model can be used to examine the impact of contact stimuli on cellular reversals. The basic model construction relies on the presence of two nested feedback circuits, which prompted us to reexamine the behavior of M. xanthus cells. We performed experiments to test the model, and this cell analysis challenges previous assumptions of 30 to 60 min reversal periods in frzCD, frzF, frzE, and frzZ mutants. We demonstrate that this average reversal period is an artifact of the method employed to record reversal data, and that in the absence of signal from the Frz pathway, Mgl components can occasionally reverse the cell near wildtype periodicity, but frz- cells are otherwise in a long nonoscillating state.
    ... Sissi, C., Rossi, P., Felluga, F., Formaggio, F., Palumbo, M., Tecilla, P., Toniolo, C. and Scrimin, P. (2001) Dinuclear Zn2+ complexes of synthetic heptapeptides as ... Yang, Q., Xu, JQ, Sun, YS, Li, ZG, Li, YG and Qian, XH (2006)... more
    ... Sissi, C., Rossi, P., Felluga, F., Formaggio, F., Palumbo, M., Tecilla, P., Toniolo, C. and Scrimin, P. (2001) Dinuclear Zn2+ complexes of synthetic heptapeptides as ... Yang, Q., Xu, JQ, Sun, YS, Li, ZG, Li, YG and Qian, XH (2006) Hydrolysis of plasmid DNA and RNA by amino alkyl ...
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    ABSTRACT By combining the physics of gels with the hydrodynamics of two-phase fluids, we construct a set of equations that describe the hydration dynamics of polyelectrolyte gels. Numerical solutions to these equations are consistent with... more
    ABSTRACT By combining the physics of gels with the hydrodynamics of two-phase fluids, we construct a set of equations that describe the hydration dynamics of polyelectrolyte gels. Numerical solutions to these equations are consistent with previous theory and experiments on gel swelling, but extend the physics to include the flow of the fluid solvent as well as treating the fluid and solvent equally. We use our equations to derive the effective diffusion constants for neutral and charged spherically distributed gels in terms of more microscopic paramters. We then solve the novel probelm of calculating the swelling of an isotropic, spherical gel with a permeable boundary condition and compare these results to previous experimetns on swelling gels.
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    ABSTRACT Crawling eukaryotic cells play many roles in biology. White blood cells chemotactically track down pathogens. Fibroblasts crawl and pull skin back together during wound healing. Cancer cells become metastatic and migrate to other... more
    ABSTRACT Crawling eukaryotic cells play many roles in biology. White blood cells chemotactically track down pathogens. Fibroblasts crawl and pull skin back together during wound healing. Cancer cells become metastatic and migrate to other points in the body. Therefore, understanding the physical mechanism driving crawling motility is very important. In crawling cells, a polymer meshwork, usually composed of actin filaments, provides both the structural integrity of the cell and is reponsible for the force production during migration. We present a theory that describes the dynamics of this actin gel and apply it to the crawling motility of nematode sperm cells. This model maintains the shape of the cell during crawling as occurs during the migration of Ascaris suum spermatozoa and also produces forces comparable to what has been measured in other crawling cells.
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    We present here a procedure for growing lipid tubules in vitro. This method allows us to grow tubules of consistent shape and structure, and thus can be a useful tool for nano-engineering applications. There are three stages during the... more
    We present here a procedure for growing lipid tubules in vitro. This method allows us to grow tubules of consistent shape and structure, and thus can be a useful tool for nano-engineering applications. There are three stages during the tubule growth process: initiation, elongation and termination. Balancing the forces that act on the tubule head shows that the growth of tubules during the elongation phase depends on the balance between osmotic pressure and the viscous drag exerted on the membrane from the substrate and the external fluid. Using a combination of mathematical modelling and experiment, we identify the key forces that control tubule growth during the elongation phase.
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    The bacterial flagellar motor (BFM) is responsible for driving bacterial locomotion and chemotaxis, fundamental processes in pathogenesis and biofilm formation. In the BFM, torque is generated at the interface between transmembrane... more
    The bacterial flagellar motor (BFM) is responsible for driving bacterial locomotion and chemotaxis, fundamental processes in pathogenesis and biofilm formation. In the BFM, torque is generated at the interface between transmembrane proteins (stators) and a rotor. It is well established that the passage of ions down a transmembrane gradient through the stator complex provides the energy for torque generation. However, the physics involved in this energy conversion remain poorly understood. Here we propose a mechanically specific model for torque generation in the BFM. In particular, we identify roles for two fundamental forces involved in torque generation: electrostatic and steric. We propose that electrostatic forces serve to position the stator, whereas steric forces comprise the actual "power stroke." Specifically, we propose that ion-induced conformational changes about a proline "hinge" residue in a stator α-helix are directly responsible for generating the power stroke. Our model predictions fit well with recent experiments on a single-stator motor. The proposed model provides a mechanical explanation for several fundamental properties of the flagellar motor, including torque-speed and speed-ion motive force relationships, backstepping, variation in step sizes, and the effects of key mutations in the stator.
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    Intracellular organelles have characteristic pH ranges that are set and maintained by a balance between ion pumps, leaks, and internal ionic equilibria. Previously, a thermodynamic study by Rybak et al. (Rybak, S., F. Lanni, and R.... more
    Intracellular organelles have characteristic pH ranges that are set and maintained by a balance between ion pumps, leaks, and internal ionic equilibria. Previously, a thermodynamic study by Rybak et al. (Rybak, S., F. Lanni, and R. Murphy. 1997. Biophys. J. 73:674-687) identified the key elements involved in pH regulation; however, recent experiments show that cellular compartments are not in thermodynamic equilibrium. We present here a nonequilibrium model of lumenal acidification based on the interplay of ion pumps and channels, the physical properties of the lumenal matrix, and the organelle geometry. The model successfully predicts experimentally measured steady-state and transient pH values and membrane potentials. We conclude that morphological differences among organelles are insufficient to explain the wide range of pHs present in the cell. Using sensitivity analysis, we quantified the influence of pH regulatory elements on the dynamics of acidification. We found that V-ATPase proton pump and proton leak densities are the two parameters that most strongly influence resting pH. Additionally, we modeled the pH response of the Golgi complex to varying external solutions, and our findings suggest that the membrane is permeable to more than one dominant counter ion. From this data, we determined a Golgi complex proton permeability of 8.1 x 10(-6) cm/s. Furthermore, we analyzed the early-to-late transition in the endosomal pathway where Na,K-ATPases have been shown to limit acidification by an entire pH unit. Our model supports the role of the Na,K-ATPase in regulating endosomal pH by affecting the membrane potential. However, experimental data can only be reproduced by (1) positing the existence of a hypothetical voltage-gated chloride channel or (2) that newly formed vesicles have especially high potassium concentrations and small chloride conductance.
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    Certain biological experiments investigating cell motion result in time lapse video microscopy data which may be modeled using stochastic differential equations. These mod- els suggest statistics for quantifying experimental results and... more
    Certain biological experiments investigating cell motion result in time lapse video microscopy data which may be modeled using stochastic differential equations. These mod- els suggest statistics for quantifying experimental results and testing relevant hypotheses, and carry implications for the qualitative behavior of cells and for underlying biophysical mech- anisms. Directional cell motion in response to a stimulus, termed taxis, has
    ABSTRACT Evolution has created a class of proteins that have the ability to convert chemical energy into mechanical force. Some of these use the free energy of nucleotide hydrolysis as fuel, while others employ ion gradients. Some are... more
    ABSTRACT Evolution has created a class of proteins that have the ability to convert chemical energy into mechanical force. Some of these use the free energy of nucleotide hydrolysis as fuel, while others employ ion gradients. Some are “walking motors,” others rotating engines. Some are reversible; others are unidirectional. Could there be any common principles among such diversity?
    Adsorption of proteins onto membranes can alter the local membrane curvature. This phenomenon has been observed in biological processes such as endocytosis, tubulation, and vesiculation. However, it is not clear how the local surface... more
    Adsorption of proteins onto membranes can alter the local membrane curvature. This phenomenon has been observed in biological processes such as endocytosis, tubulation, and vesiculation. However, it is not clear how the local surface properties of the membrane, such as membrane tension, change in response to protein adsorption. In this article, we show that the partial differential equations arising from classical elastic model of lipid membranes, which account for simultaneous changes in shape and membrane tension due to protein adsorption in a local region, cannot be solved for nonaxisymmetric geometries using straightforward numerical techniques; instead, a viscous-elastic formulation is necessary to fully describe the system. Therefore, we develop a viscous-elastic model for inhomogeneous membranes of the Helfrich type. Using the newly available viscous-elastic model, we find that the lipids flow to accommodate changes in membrane curvature during protein adsorption. We show that, at the end of protein adsorption process, the system sustains a residual local tension to balance the difference between the actual mean curvature and the imposed spontaneous curvature. We also show that this change in membrane tension can have a functional impact such as altered response to pulling forces in the presence of proteins.
    The forces that drive sea urchin primary invagination remain mysterious. To solve this mystery we have developed a set of finite element simulations that test five hypothesized mechanisms. Our models show that each of these mechanisms can... more
    The forces that drive sea urchin primary invagination remain mysterious. To solve this mystery we have developed a set of finite element simulations that test five hypothesized mechanisms. Our models show that each of these mechanisms can generate an invagination; however, the mechanical properties of an epithelial sheet required for proper invagination are different for each mechanism. For example, we
    Summary Since the days of van Leeuwenhoek in the 1600s, cell biologists have marveled at how cells crawl. Although much is understood about the contractile forces generated at the leading edge of the crawling cell, little is known about... more
    Summary Since the days of van Leeuwenhoek in the 1600s, cell biologists have marveled at how cells crawl. Although much is understood about the contractile forces generated at the leading edge of the crawling cell, little is known about the retraction force at the rear of the ...
    The motility of some kinds of bacteria depends on their spiral form, as does the virulence of certain pathogenic species. We propose a novel mechanism for the development of spiral shape in bacteria and the supercoiling of chains... more
    The motility of some kinds of bacteria depends on their spiral form, as does the virulence of certain pathogenic species. We propose a novel mechanism for the development of spiral shape in bacteria and the supercoiling of chains ('filaments') of many cells. Recently discovered actin-like proteins lying just under the cell wall form fibers that play a role in maintaining cell shape. Some species have a single actin-like fiber helically wrapped around the cell, while others have two fibers wrapped in the same direction. Here, we show that if these fibers elongate more slowly than growth lengthens the cell, the cell both twists and bends, taking on a spiral shape. We tested this mechanism using a mathematical model of expanding fiber-wound structures and via experiments that measure the shape changes of elongating physical models. Comparison of the model with in vivo experiments on stationary phase Caulobacter crescentus filaments provide the first evidence that mechanical s...
    After a first encounter with most antigens, the immune system responds to subsequent encounters with a faster, more efficient and more strenuous antibody response. The memory of previous antigen contacts is carried by lymphocytes.... more
    After a first encounter with most antigens, the immune system responds to subsequent encounters with a faster, more efficient and more strenuous antibody response. The memory of previous antigen contacts is carried by lymphocytes. Expanding on the model developed in Part I of this paper, we examine the optimal strategy available to the immune system for B memory cell production. We again find that the strategy should be of the bang-bang variety.
    ... Acad. Sci. USA 81, 161-164 (1984) De Gennes, P.: Dynamics of entangled polymer solutions I. The Rouse Model. ... Cell Biophys. 4, 177-209 (1983) Odell, G., Oster, G., Burnside, B., Alberch, P.: The mechanical basis of morphogenesis I:... more
    ... Acad. Sci. USA 81, 161-164 (1984) De Gennes, P.: Dynamics of entangled polymer solutions I. The Rouse Model. ... Cell Biophys. 4, 177-209 (1983) Odell, G., Oster, G., Burnside, B., Alberch, P.: The mechanical basis of morphogenesis I: Epithelial folding and invagination. Devel. ...
    The pentameric ATPase motor gp16 packages double-stranded DNA into the bacteriophage phi29 virus capsid. On the basis of the results of single-molecule experimental studies, we propose a push and roll mechanism to explain how the... more
    The pentameric ATPase motor gp16 packages double-stranded DNA into the bacteriophage phi29 virus capsid. On the basis of the results of single-molecule experimental studies, we propose a push and roll mechanism to explain how the packaging motor translocates the DNA in bursts of four 2.5 bp power strokes, while rotating the DNA. In this mechanism, each power stroke accompanies P(i) release after ATP hydrolysis. Since the high-resolution structure of the gp16 motor is not available, we borrowed characterized features from the P4 RNA packaging motor in bacteriophage phi12. For each power stroke, a lumenal lever from a single subunit is electrostatically steered to the DNA backbone. The lever then pushes sterically, orthogonal to the backbone axis, such that the right-handed DNA helix is translocated and rotated in a left-handed direction. The electrostatic association allows tight coupling between the lever and the DNA and prevents DNA from slipping back. The lever affinity for DNA de...
    ... 2185 The biophysics of DNA hybridization with immobilized oligonucleotide probes. Vincent Chan, David J. Graves, and Steven E. McKenzie..... ... Knut Debus, Jana Hartmann, Gordan Kilic, and Manfred Lindau..... 2808 ...
    ... If the herbivore is a defoliator, then the parameter function p~ in [2] depends also on ... depend on F(t,a,m). As an illustration of the formulation of plant-herbivore interaction models ... less demonstrable as an infinite... more
    ... If the herbivore is a defoliator, then the parameter function p~ in [2] depends also on ... depend on F(t,a,m). As an illustration of the formulation of plant-herbivore interaction models ... less demonstrable as an infinite combination of timing, defoliation severity, and fruit attack rates exist ...
    Sperm of the nematode, Ascaris suum, crawl using lamellipodial protrusion, adhesion and retraction, a process analogous to the amoeboid motility of other eukaryotic cells. However, rather than employing an actin cytoskeleton to generate... more
    Sperm of the nematode, Ascaris suum, crawl using lamellipodial protrusion, adhesion and retraction, a process analogous to the amoeboid motility of other eukaryotic cells. However, rather than employing an actin cytoskeleton to generate locomotion, nematode sperm use the ...
    Human keratinocytes migrate towards the negative pole in DC electric fields of physiological strength. This directional migration is promoted by epidermal growth factor (EGF). To investigate how EGF and its receptor (EGFR) regulate this... more
    Human keratinocytes migrate towards the negative pole in DC electric fields of physiological strength. This directional migration is promoted by epidermal growth factor (EGF). To investigate how EGF and its receptor (EGFR) regulate this directionality, we first examined the effect of protein tyrosine kinase inhibitors, including PD158780, a specific inhibitor for EGFR, on this response. At low concentrations, PD158780 inhibited keratinocyte migration directionality, but not the rate of migration; at higher concentrations, it reduced the migration rate as well. The less specific inhibitors, genistein, lavendustin A and tyrphostin B46, reduced the migration rate, but did not affect migration directionality. These data suggest that inhibition of EGFR kinase activity alone reduces directed motility, and inhibition of multiple tyrosine kinases, including EGFR, reduces the cell migration rate. EGFR redistribution also correlates with directional migration. EGFR concentrated on the cathodal face of the cell as early as 5 minutes after exposure to electric fields. PD158780 abolished EGFR localization to the cathodal face. These data suggest that EGFR kinase activity and redistribution in the plasma membrane are required for the directional migration of keratinocytes in DC electric fields. This study provides the first insights into the mechanisms of directed cell migration in electric fields.
    Prestin is a critical component of the motor complex that generates forces and dimensional changes in cells in response to changes in the cell transmembrane potential. We propose an electro-diffusion model to reveal the frequency and... more
    Prestin is a critical component of the motor complex that generates forces and dimensional changes in cells in response to changes in the cell transmembrane potential. We propose an electro-diffusion model to reveal the frequency and voltage dependence of electric charge transfer by prestin. The movement of the combined charge (including chloride ion and protein charges) across the membrane is
    ... THE VELIGER © CMS, Inc., 1986 A Model for Shell Patterns Based on Neural Activity by BARD ERMENTROUT ... 28, No.4 a b c Figure 1 Three fundamental classes of shell pigment markings on Bankivia fasciata: a, longitudinal bands; b,... more
    ... THE VELIGER © CMS, Inc., 1986 A Model for Shell Patterns Based on Neural Activity by BARD ERMENTROUT ... 28, No.4 a b c Figure 1 Three fundamental classes of shell pigment markings on Bankivia fasciata: a, longitudinal bands; b, incremental lines; c, oblique stripes. ...
    Molecular motors convert chemical energy into mechanical force and movement. Operating at energies just above those of the thermal bath, these motors experience large fluctuations, and their physical description must be necessarily... more
    Molecular motors convert chemical energy into mechanical force and movement. Operating at energies just above those of the thermal bath, these motors experience large fluctuations, and their physical description must be necessarily stochastic. Here, motor operation is described as a biased diffusion on a potential energy surface defined by the interactions of the motor with its track and its fuel. These ideas are illustrated with a model of the rotary movement of the F(o) motor.
    The two-headed motor protein kinesin hydrolyzes nucleotide to move unidirectionally along its microtubule track at speeds up to 1000 nm/s (Saxton et al., 1988) and develops forces in excess of 5 pN (Hunt et al., 1994; Svoboda et al., 1... more
    The two-headed motor protein kinesin hydrolyzes nucleotide to move unidirectionally along its microtubule track at speeds up to 1000 nm/s (Saxton et al., 1988) and develops forces in excess of 5 pN (Hunt et al., 1994; Svoboda et al., 1 994a). Individual kinesin molecules ...
    MONOGRAPHS IN POPULATION HIOLOGY KDTIT.I) PV ROm.RT M. MAY 1. The Theory of Island Biogeography, by Robert H. MacArthur and Kdward O. \Vilson 2. Involution in Changing Knvironments: Sonic I heorctical Ex- plorations, hy Richard Kevins 3.... more
    MONOGRAPHS IN POPULATION HIOLOGY KDTIT.I) PV ROm.RT M. MAY 1. The Theory of Island Biogeography, by Robert H. MacArthur and Kdward O. \Vilson 2. Involution in Changing Knvironments: Sonic I heorctical Ex- plorations, hy Richard Kevins 3. Adaptive Geometry ...