Structure and Classification of Viruses
🌊Introduction🌊
Viruses are microscopic, non-cellular organisms that can infect plants, animals, and bacteria. They are considered as a connecting link between living and non-living things because they remain inactive outside the host cell but become active inside the host cell.
What are Viruses?Viruses are obligate intracellular parasites. They cannot reproduce on their own and depend completely on a living host cell for multiplication.
They were first discovered by D.J. Ivanowsky (1892) while studying tobacco mosaic disease.Characteristics of Viruses:
* Viruses are non-cellular organisms.* They are inactive outside the host cell.
* They contain genetic material either DNA or RNA.
* No virus contains both DNA and RNA together.
* They reproduce only inside living cells.
* Viruses are extremely small and can pass through bacteria-proof filters.
* They can be crystallized.
Structure of Virus:
A virus mainly consists of two parts:
1. Genetic Material
The genetic material may be:
* DNA* RNA
2. Capsid
The protein coat surrounding the nucleic acid is called the capsid.
Capsid is made up of small units called capsomeres.
Types of Viruses Based on Host:
Plant Viruses* Usually contain single-stranded RNA.
Example: Tobacco Mosaic Virus (TMV)
Animal Viruses
* May contain single or double-stranded DNA or RNA.
Bacterial Viruses (Bacteriophages)
* Infect bacteria.
* Usually contain double-stranded DNA.
Classification of Viruses:
Viruses can be classified on different bases:
Based on Shape
* Helical viruses
* Polyhedral viruses
* Complex viruses
Based on Host
*Plant viruses
*Animal viruses
*Bacterial viruses
Based on Genetic Material
* DNA viruses
* RNA viruses
Bacteriophage Structure
A bacteriophage contains:
* Collar
* Sheath
* Tail fibres
It infects bacterial cells and injects its genetic material into the host.
Tobacco Mosaic Virus (TMV)
Diseases Caused by Viruses
Viruses cause many diseases such as:* Common cold
* Influenza
* Herpes
* AIDS
* Smallpox
Why are Viruses Called Living and Non-living?
Living Characters* Reproduce inside host cells
* Possess genetic material
Non-living Characters
* Can be crystallized
* Inactive outside the host body
Conclusion
Viruses are unique infectious agents that show both living and non-living characteristics. Their structure includes genetic material and a protective protein coat called capsid. Viruses are classified based on shape, host, and genetic material.
FAQs
What is a virus?A virus is a microscopic non-cellular organism that can reproduce only inside a living host cell.
Why are viruses called obligate parasites?
Viruses depend completely on host cells for reproduction and metabolism, so they are called obligate parasites.
What are the main parts of a virus?
The main parts of a virus are genetic material (DNA or RNA) and a protein coat called capsid.
What is a capsid?
Capsid is the protective protein coat surrounding the genetic material of a virus.
What is a bacteriophage?
A bacteriophage is a virus that infects bacterial cells.
Does a virus contain both DNA and RNA?
No, a virus contains either DNA or RNA, but never both together.
What is TMV?
TMV (Tobacco Mosaic Virus) is a plant virus containing single-stranded RNA.
Are viruses living or non-living?
Viruses show both living and non-living characteristics. They are inactive outside the host cell but active inside it.
How are viruses classified?
Viruses are classified based on shape, host organism, and genetic material.
Which virus infects bacteria?
Bacteriophages infect bacteria.
1. Who discovered viruses?
Correct Answer: B. D.J. Ivanowsky
2. Viruses are:
Correct Answer: B. Non-cellular organisms
3. The protein coat of a virus is called:
Correct Answer: B. Capsid
4. Which virus infects bacteria?
Correct Answer: C. Bacteriophage
5. TMV contains:
Correct Answer: B. Single-stranded RNA
6. Viruses reproduce only inside:
Correct Answer: C. Living host cells
7. Which of the following is a plant virus?
Correct Answer: B. TMV
8. Viruses contain:
Correct Answer: B. Either DNA or RNA
9. Capsomeres are:
Correct Answer: B. Protein subunits of capsid
10. Viruses are called connecting links between living and non-living because:
Correct Answer: C. They show both living and non-living characteristics
0 Comments