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What is quasi-equivalence?

Quasi-equivalence can be defined as the extent of similarity between these structurally unique environments occupied by the chemically identical subunits in the virus capsid. Quasi-equivalent capsids should contain 60T subunits, however, there are exceptions.

Why do viruses have icosahedral symmetry?

However, we have found that the presence of a small compression of the capsid (caused, for instance, by an external pressure, or a genome size smaller that the preferred size of the capsid protein shell, or a longer-range attractive interaction between capsomers) systematically facilitates the appearance of icosahedral …

What is H and K in triangulation number?

The triangulation number is defined as the square of the distance between 2 adjacents 5-fold vertices. Point O corresponds to a 5-fold vertex and the first neighbouring 5-fold vertex,at point M has coodinates (H,K).

What is the advantage of icosahedral symmetry?

Thus, the advantages of icosahedral symmetry come with costs – subunit geometry must be ideal, subunit interaction energies have a relatively narrow window, and the resulting capsids’ resistance to dissociation makes them peculiarly unresponsive to its environment.

Is influenza helical or icosahedral?

In fact, most plant viruses are helical, and it is very uncommon that a helical plant virus is enveloped. In contrast, all helical animal viruses are enveloped. These include well-known viruses such as influenza virus, measles virus, mumps virus, rabies virus, and Ebola virus (Fig. 2.5 ).

What is symmetry virus?

Self assembly of virus capsids follows two basic patterns: helical symmetry, in which the protein subunits and the nucleic acid are arranged in a helix, and icosahedral symmetry, in which the protein subunits assemble into a symmetric shell that covers the nucleic acid-containing core.

What is t number virus?

The capsid is composed 60 asymmetric units made of 1 protein (T=1), for a total of 60 capsid proteins. Icosahedric triangulation number is calculated following Caspar and Klug system. Physical principles in the construction of regular viruses.

What is the difference between helical and icosahedral viruses?

A helix is mathematically defined by amplitude and pitch. An icosahedron is a geometric shape with 20 sides, each composed of an equilateral triangle. The sides are composed of viral protein subunits that create a structural unit, which is repeated to form a larger side and the other sides of the icosahedron.

How many edges does the icosahedral virus have?

30 edges
The 20 faces of the icosahedron are equilateral triangles; they meet in 30 edges and 12 vertices.