VIRUSES AND ITS TYPES

 TYPES OF VIRUS STRUCTURES: 

The structure of a virus varies greatly depending on its function. From a simple outer covering made up of proteins, to a complex formation consisting of a head and tail, there are four different types of viruses. Each one, though extremely microscopic, has its own unique features, which help in its functioning. 



The Different Types of Virus Structures are:

1. Helical Virus
2. Envelope Virus
3. Icosahedral Virus
4. Complex Virus

HELICAL VIRUS: 

This type of virus has a capsid made up of a single type of protein sample stacked around an axis to form a type of helix structure. This structure may have a hollow center, making it look like a tube. 

This arrangement leads to this type of virion having a rod-like structure. The nucleic acid is arranged in the central cavity. They are usually 15-19 nm wide and range in length from 300-500 nm long, depending on the nucleic acid. An example for such virus is the Tobacco Mosaic Virus (TMV). 

Helical Structure of a virus


ENVELOPE VIRUS:

Some virus samples have an additional layer of covering made from the host’s cell membrane. These type of viruses are known are enveloped virus. The membrane layer is a lipid bilayer. The membrane is studded with proteins, coded by both the host’s genome and the virus genome. Most enveloped viruses depend on their envelopes to infect hosts. The proteins in the molecules contain glycoprotein. Glycoprotein is a substance that acts as a receptor in viruses. These receptors, allow the host to bind to it, allowing it to infect the host’s cell. Examples of enveloped virus are the HIV virus and the Hepatitis C virus. 


Enveloped Virus structure


ICOSAHEDRAL:

At low magnification, these viruses appear spherical. But in reality they are arranged in a triangular geometrical pattern, similar to a soccer ball. An Icosahedron is a three dimensional shape made up of 20 triangles. The triangular sides of the capsid are made up of identical protein sub-units. It is a hollow structure, with space inside for the virus genome. When the cell dies, viruses with icosahedral structures are released into the environment, where it is broken down. An example for viruses with icosahedral structures is Adenovirus. 

Icosahedral Virus structure


COMPLEX VIRUS: 

These viruses have a unique structure. It consists of a combination of the helical and icosahedral structures. It has a head-tail morphology like structure where the head portion is composed of a icosahedral shape and the tail portion is a helical shape. This type of head-tail morphology structure is unique to viruses that infect bacteria. The virus uses its tail to create a hole in the cell wall of the bacteria and injects its genome from the head using the tail as a passage. One of its examples, the poxvirus is one of the biggest viruses and has a complex structure with a unique capsid. Example for such poxvirus is the smallpox.

Complex Virus Structure




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