Virus

 

Characteristics of virus

The word virus is taken from Latin language meaning poison. Viruses are parasitic, very minute, infectious agents. They lack cellular structure and metabolic activities. They cannot reproduce outside living cells. They are metabolically inactive outside the host cell because they don't have enzyme systems and protein synthesis machinery.

 Branch of biology that deals with the study of viruses is called virology. Father of virology - Stanley

Characters of virus

• All viruses are the smallest and simplest organism which can be observed only by the use of electron microscopes.
• They are metabolically inactive outside the host cell because they do not have enzyme systems and protein synthesis machinery.
• They are obligate parasites because They are metabolically inactive outside the host .
• . They consist of protein and nucleic acid as genetic material. The nucleic acid is generally DNA or RNA.
• The protein surrounds the nucleic acid called protein coat or capsid.
• They are acellular i.e., cellular structure is absent. So they lack nucleus, cytoplasm and cytoplasmic organelles like mitochondria, golgi complex etc.
• They can transfer the disease to plants and animals.
• . They respond to light, chemicals and temperature.
• They can show mutations like the living organism.
• Viruses can grow and reproduce within the host cell only.
• They lack enzyme systems and do not have metabolic activities of their own.
• Some viruses can be crystallized like a chemical substance.

Living characters of viruses 

• They can grow and multiply within the host cell.
• They can infect healthy organisms and are capable of spreading diseases.
• They respond to chemicals, light and temperature.
• Viruses can show mutation. 
• They contain nucleic acid either DNA or RNA, as their genetic material.
• They can transfer diseases in plants and animals.
• Replication of DNA and transcription of RNA takes place in viruses. 

Non living characters of viruses 

• Viruses are found in crystalline form outside the host.
• They don't have cellular organization. so cellular components like cell membrane, cytoplasm, nucleus and other cell organelles are absent.
• They cannot reproduce outside the host.
• They do not show metabolic activities like respiration, excretion.
• They do not show any life function without a proper host.
• They depend upon the living host for their existence
• They lack enzyme systems, so they do not have any metabolic activity of their own.
• They can be preserved in bottles like the chemicals for many years.

On the basis of host, virus are of three types i.e., 1. Plant virus - infects plants 2. Animal virus -. Infects animal 3. Bacteriophage virus - infects bacteria

On the basis of their nucleic acid, virus are of following types: 1. DNA virus 2. RNA virus 3. DNA - RNA virus

Economic importance of virus  

Useful activities of virus

• Tulip Mosaic virus makes the Tulip flower attractive which can be sold at a high price .
• Virus is also used to transfer the gene from one bacterium to another in genetic engineering . 
• Some viruses may destroy the bacterial cells and make water free from bacteria.
• They are widely used in genetic research .
• Bacteriophage viruses are used in the treatment of several bacterial diseases like cholera, dysentery plague etc. 

Harmful activities of virus: 

Diseases to animals:

           Name of disease  :    Virus

1. Coronavirus disease :  Coronavirus ( covid-19) 
2. AIDS  :  HIV virus
3. Common cold : Rhinovirus
4. Influenza :  Influenza virus
5. Polio  :  Polio virus
6. Hepatitis B :  Hepatitis B virus
7. Ebola : Ebola virus
8. Mumps : Paramyxovirus 

Disease to plants: 

           Name of disease    :    Virus

1.  Tobacco mosaic :  Tobacco mosaic virus (TMV)
2.  Leaf roll of potato :  Solanum virus
3. Potato Crinkle :  Virus X and Virus A
4. Tomato Leaf curl : Tomato Leaf curl virus

                                         Fig : Bacteriophage virus