Cytoskeleton influence on normal and tangent fluctuation modes in the red blood cells

We argue that the paradoxal softness of the red blood cells (RBC) in fluctuation spectra experiments is apparent. We show that the effective surface shear modulus $\mu_s$ of the RBC obtained from fluctuation data and that measured in static deformation experiments have the same order of magnitude. A simple micromechanical model of the RBC developped for this purpose accounts for the influence of a finite-thickness cytoskeleton on the fluctuations of the composite membrane-cytoskeleton system. The spectrin network cytoskeleton with the bulk shear modulus estimated as $\mu\approx105\div 165$ Pa contributes to both normal and tangent fluctuations of the system and confines the fluctuations of the lipid membrane. The ratio of mean square amplitudes of the RBC normal and tangent fluctuations $/$ calculated in the frame of the model is 2-3 orders of magnitude smaller that it is in the free membrane with the same bending and shear moduliComment: 14 pages, 4 figure

Structures of Spherical Viral Capsids as Quasicrystalline Tilings

Spherical viral shells with icosahedral symmetry have been considered as quasicrystalline tilings. Similarly to known Caspar-Klug quasi-equivalence theory, the presented approach also minimizes the number of conformations necessary for the protein molecule bonding with its neighbors in the shell, but is based on different geometrical principles. It is assumed that protein molecule centers are located at vertices of tiles with identical edges, and the number of different tile types is minimal. Idealized coordinates of nonequivalent by symmetry protein positions in six various capsid types are obtained. The approach describes in a uniform way both the structures satisfying the well-known Caspar-Klug geometrical model and the structures contradicting this model.Comment: 8 pages, 2 figures; This version was published in Physics of the Solid State, 2015, Vol. 57, No.4, pp. 810-81