Protrusion force

Figure 4. The Brownian ratchet model of lamellar protrusion (Peskin et al., 1993). According to this hypothesis, the distance between the plasma membrane (PM) and the filament end fluctuates randomly. At a point in time when the PM is most distant from the filament end, a new monomer is able to add on. Consequently, the PM is no longer able to return to its former position since the filament is now longer. The filament cannot be pushed backwards by the returning PM as it is locked into the mass of the cell cortex by actin binding proteins. In this way, the PM is permitted to diffuse only in an outward direction. The maximum force which a single filament can exert (the stalling force) is related to the thermal energy of the actin monomer by kinetic theory according to the following equation ...

As the stamp is gently placed in contact with a solution spread on a substrate, capillary forces drive the solution to form menisci under the stamp protrusions. The solution remains pinned to the protrusions upon solvent evaporation. As the critical concentration is reached, the solute precipitates from solution onto the substrate, giving rise to a structured thin film replicating the protrusion of the stamp. By optimizing the conditions, it is possible to print isolated structures with a size comparable to or even smaller than the lateral width of the stamp protrusions,... 

In summary, our findings suggest that cholesterol and certain analogs are a highly valuable neutral lipid component ( helper lipid ) for CL-DNA complexes because they facilitate endosomal escape by reducing the repulsive hydration and protrusion forces. They are thus able to lower the kinetic barrier for fusion of the cationic membranes of CL-DNA complexes with the anionic membrane of the endosome and increase TE, in addition to their beneficial effect on aM. 

Evidence for a specific retraction force in Ascaris sperm was obtained by exploiting the sensitivity of the MSP cytoskeleton to changes in intracellular pH to uncouple protrusion of the leading edge from retraction of the cell body (Italiano et al., 1999). Lowering intracellular pH in sperm below... 

The principles of the push-pull model probably apply generally to amoeboid cell motility. Indeed, a consensus is developing that in both sperm and actin-based crawling cells the force for protrusion is derived from localized cytoskeletal assembly (reviewed by Pollard and Borisy, 2003). However, as applied to nematode sperm locomotion, the model envisions that lamellipod extension and cell body retraction are linked reciprocally to the polymerization state of the cytoskeleton. The lack of structural polarity of MSP filaments, the precise localization of cytoskeletal polymerization and depolymerization at opposite ends of the fiber complexes, and insights gained from reconstitution of cytoskeletal dynamics and motility in vitro and in vivo all support the conclusion that nematode sperm move without using motor proteins and that, instead, they rely on... 

FIGURE 1.14. Schematic representation of the pattern replication process. The topography of the top plate induced a lateral force gradient that focuses the instability towards the downward pointing protrusions of the master plate. 

Remarkably, the connection between a force between spheres and an energy between planes holds for the fullest expression of Gpp(/). In the regime of large radii compared with minimal separation, this relation can also hold for other curved surfaces or protrusions having gradual local spherical curvature. 

Another model [27] attempted to explain only the hydration interactions between neutral phospholipid bilayers, because those interactions appear to be quite different from the hydration forces determined in other systems they have a much shorter decay length and are almost independent of electrolyte concentration [11], The theory was based on a steric repulsion between lipid molecules, which protruding from one bilayer collide with the molecules of the opposite bilayer [27]. However, it was shown that the hydration interactions are not affected much by the polymerization of bilayers, which essentially exclude molecular protrusions [28]. 

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