Tobacco mosaic virus length

Some virus particles have their protein subunits symmetrically packed in a helical array, forming hollow cylinders. The tobacco mosaic virus (TMV) is the classic example. X-ray diffraction data and electron micrographs have revealed that 16 subunits per turn of the helix project from a central axial hole that runs the length of the particle. The nucleic acid does not lie in this hole, but is embedded into ridges on the inside of each subunit and describes its own helix from one end of the particle to the other. 

A typical virus with helical symmetry is the tobacco mosaic virus (TMV). This is an RNA virus in which the 2130 identical protein subunits (each 158 amino acids in length) are arranged in a helix. In TMV, the helix has 16 1/2 subunits per turn and the overall dimensions of the virus particle are 18 X 300 nm. The lengths of helical viruses are determined by the length of the nucleic acid, but the width of the helical virus particle is determined by the size and packing of the protein subunits. 

This theory clearly predicts that the shape of the polymer length distribution curve determines the shape of the time course of depolymerization. For example Kristofferson et al. (1980) were able to show that apparent first-order depolymerization kinetics arise from length distributions which are nearly exponential. It should also be noted that the above theory helps one to gain a better feeling for the time course of cytoskeleton or mitotic apparatus disassembly upon cooling cells to temperatures which destabilize microtubules and effect unidirectional depolymerization. Likewise, the linear depolymerization kinetic model could be applied to the disassembly of bacterial flagella, muscle and nonmuscle F-actin, tobacco mosaic virus, hemoglobin S fibers, and other linear polymers to elucidate important rate parameters and to test the sufficiency of the end-wise depolymerization assumption in such cases. 

Nuclei of Mammalian Cells -— Length of Tobacco Mosaic Virus... 

Fig. 6. The hydrodynamic lengths of a tobacco mosaic virus sample. Reproduced from Yang (1961a).

Brownian rod-like objects of high aspect ratio are usually molecules, not colloidal particles. As exception is tobacco mosaic virus (TMV), which is a Brownian particle of length 300 nm and diameter 18 nm (Caspar 1963). For completeness, we shall discuss the theory of Brownian rod-like particles in this chapter, with the understanding that the theory for such particles is actually more relevant to long stiff molecules than to rod-like fibers. The behavior of non-Brownian fiber suspensions is covered in Section 6.3.2.2.------------------... 

FIGURE 10.17 Stereodiagram of a segment of helical double-stranded RNA, seven base pairs in length, is shown superimposed on its corresponding difference electron density derived from crystalline satelhte tobacco mosaic virus. 

Some viruses such as the tobacco mosaic virus (TMV) can form lyotropic cholesteric liquid crystals. TMV contains 94% protein and 6% RNA. In TMV the proteins and RNA are stacked regularly, see Figure 6.26. It looks like a long rod of average length 300 nm and of diameter 15 nm. The molecular mass is as high as 4 x 107. 

Certain macromolecular species are modeled more accurately as a cylinder rather than an ellipsoid. Examples include short DNA fragments and rodlike viruses such as tobacco mosaic virus (TMV). Extensive theoretical studies of the hydrodynamic properties of cylindrical particles have been carried out. These have been recently reviewed by Ortega and de la Torre [2003], who have extended prior calculations using the bead-shell model to short cylinders and disks. Eor long cylinders of length L and cross-sectional diameter d, and hence axial ratio J=Lid, such analysis leads to... 

Viruses with helical symmetry, or "linear" viral capsids, have their genetic material encased in a helix of identical protein subunits, the length of whieh is determined by the length of the encased nucleic acid. There are three main classes of simple helical viruses the rigid rod viruses, the flexuous plant viruses, and the filamentous bacteriophage-.-TTi e most studied of these viruses is the rigid rod Tobacco Mosaic Virus (TMV). 

For the rod-shaped particles of tobacco mosaic virus of length 280 nm at room temperature, for example, rotational diffusion coefficients of 550 s" were found. The rods thus require 0.0018 s in order to return to their equilibrium (randomly oriented) positions. 

Unaware of the underlying principle this was first used by Cohen already in 1941 [87] to separate two viruses Tobacco Mosaic Virus and Tobacco Necrosis Virus. Tobacco Mosaic Virus is a rod-Uke vims with a length of 300 nm and diameter of 18 nm and Tobacco Necrosis Vims a spherical virus with a diameter of about 26 nm. Cohen used the polysaceharide heparin as depletant to separate these viruses. Recently, this method to separate eoUoids of different size and shape has gained new impetus. For nano-based teehnologies partieles with a specific size and shape are critical to optimize the nanostrueture-dependent optieal, electrical and magnetic properties. 

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