Structural Features of Viruses

Size of Viruses

Virus particles vary widely in size. The smallest viruses e.g. virus of foot and mouth disease  measuring about 20  mill microns are about the size of largest protein molecules. The largest viruses measuring about 350 nm are as large as the smallest bacteria (Mycoplasma).

Shape and Symmetry of Viruses

Most plant viruses are rod shaped or filamentous while the animal viruses may be filamentous or roughly spherical filamentous vireos are cylindrical structures with a helical symmetry, The most animal viruses ,the helix is highly coiled into a sub spherical structure .The spherical vireos are polyhedral structured like diamonds with  a typical  icosahedra  symmetry ,  each having 20 equilateral triangular sides or facets an 12 vertices or corners.

Poxviruses and rabies virus are unique in shape and symmetry. Poxviruses are brick shaped and rabies virus is bullet shaped. These viruses are complex in structure and symmetry.

Viruses of bacteria are also unique in shape and structure. Each vision is a tadpole shaped structure having two main parts a polyhedral headland a spring like or conical tail with a thin collar in between. The free flattened end of the tail bears a large endplate or base plate from which slender hook like legs, called   tail fibres and six small pegs or spikes project different directions. Contain bacteriophages lack the endplate, tail fibres and pages. 

Bacteriophage  Influenza Virus

           Herpes Virus                   Polio virus