Virus Structures, Capsids, Icosahedron, Helical, envelope

Virus in it complete particles, virion, made up of nucleic acid as core of it body, surrounded with a protein coats, called capsids.


Cspsid is made up of large numbers of morphological united called capsomers.

Combination of capsids with nucleic acid is known as Nucleocapsid.

Capsomers are arranged symmetrical around the core.

Capsids perform two Major function

1. Of the function of capsids, it render protection to virus.

2. It help the virus to enter it host, I.e animals of plants.

Arrangements of capsids

Capsids are arrange in two symmetrical around the core. Which Are.

1. Icosahedral Symmetry. 2. Helical Symmetry.

But virues such as Poxiviruses, have a complex structures.

Icosahedral Symmetry

Icosahedron is polygon with 12 vertices (Corner) and facet (sides).

Each facets of the Symmetry are being an equilateral to triangles, e.g. Adenovirus.

The Symmetry, usually are formed as an independent of nucleic acid.

Helical Symmetry

In helical Symmetry, the capsomers are tightly bound to the nucleic acid, to the extend the nucleic acid spread widely to for helix, unlike icosahedral Symmetry, helical Symmetry exhibit interaction between the nucleic acid core and the capsids.

Example is: Tobacco-mo-saic virus and orthomyxoviruses.

Complex Structures

Some viruses, like we mention earlier did not exhibit symmetry, such virus are referred to ad complex structures.

Poxiviruses is an example of such virus.


The virus has no Symmetry structure, but referred to complex structures.

It have brick shaped with ridges on the external surfaces.

Envelope Virus

Some virus has some covering outside their capsids, such covering is referred as envelope.

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Such virus is said to be enveloped. The envelope is derived from the cell membrane of the host which the virus entered, when the cell is released.

The envelope is made of lipids and proteins.

The protein subunits may project from the envelope as spikes.

A virus can poses different type of spikes, for example influenza has two type of spikes on it envelope, which are: Hemagglutinin and neuraminidase.

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