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7 September 2019

General Characteristics of Viruses- Microbiology |ICDS Supervisor Exam Kerala PSC

General Characteristics of Viruses- Microbiology |ICDS Supervisor Exam Kerala PSC


General Characteristics of Viruses

General Characteristics of Viruses 



The word virus, the Latin word for poison.


Viral Size Viruses range from 20 to 1000 nm in length. 



Different viruses vary considerably in size. 

Although most are quite a bit smaller than bacteria, some of the larger viruses.

For Example: Adenovirus 90 nm , Poliovirus 30 nm 


 General properties 


Viruses are inert/crystaline outside the body of host as soon as they come into the host they become living. 

They are obligatory intracellular parasites that is, they absolutely require livinghost cells in order to multiply. 

The truly distinctive features of viruses are. 

- Contain a protein coat (sometimes itself enclosed by an envelope of lipids, proteins, and carbohydrates) that surrounds the nucleic acid. 

- Multiply inside living cells by using the synthesizing machinery of the cell. 

-Cause the synthesis of specialized structures that can transfer the viral Contain a single type of nucleic acid, either DNA or RNA.

- nucleic acid to other cells. 



-Viruses have few or no enzymes of their own for metabolism; for example, they lack enzymes for protein synthesis and ATP generation. 

To multiply, viruses must take over the metabolic machinery of the host cell.


Viruses are Host Specific

 There are viruses that infect invertebrates, vertebrates, plants, protists, fungi, and bacteria. 

However, most viruses are able to infect specific types of cells of only one host species.

 In rare cases, viruses cross the host-range barrier, thus expanding their host range. 

The particular host range of a virus is determined by the virus’s requirements for its specific attachment to the host cell and the availability within the potential host of cellular factors required for viral multiplication.



 For the virus to infect the host cell, the outer surface of the virus must chemically interact with specific receptor sites on the surface of the cell.

 Viral Structure 

Viruses may be Hexagonal, Octagonal or have any other shape and have a 3D structure a virion is a complete, fully developed, infectious viral particle composed of nucleic acid and surrounded by a protein coat outside of a host cell, and is a vehicle of transmission from one host cell to another. 



Nucleic Acid 

A virus can have either DNA or RNA—but never both. The nucleic acid of a virus can be single-stranded or double-stranded. 

There are viruses with the familiar: 

- double-stranded DNA x single-stranded DNA x double-stranded RNA x single-stranded RNA




Depending on the virus, the nucleic acid can be linear or circular. 

  In some viruses (such as the influenza virus) the nucleic acid is in several separate segments. 

Capsid and Envelope 

The nucleic acid of a virus is protected by a protein coat called the capsid.



Each capsid is composed of protein subunits called capsomeres. 

In some viruses, the proteins composing the capsomeres are of a single type; in other viruses, several types of protein may be present. a particular type of virus. 

In some viruses, the capsid is covered by an envelope which usually consists of some combination of lipids, proteins, and carbohydrates., that is derived from the host cell membrane. 




Some viruses are not covered by an envelope are known as Naked Virus/non-enveloped viruses. 

The capsid of a non-enveloped virus protects the nucleic acid from nuclease enzymes in biological fluids and promotes the virus’s attachment to susceptible host cells. 

Depending on the virus, envelopes may or may not be covered by spikes, which are carbohydrate-protein complexes that project from the surface of the envelope. 

Some viruses attach to host cells by means of spikes. Spikes are such a reliable characteristic of some viruses that they can be used as a means of identification. 

The ability of certain viruses, such as the influenza virus to clump red blood cells is associated with spikes. 

Such viruses bind to red blood cells and form bridges between them. The resulting clumping is called hemagglutination.



Also Read;

Morphology of Bacteria

Anatomy of Bacteria

Vaccination -Types


This topic is important for the ICDS Supervisor Exam.Click  HERE.

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